Fix arena_get() calls that specify refresh_if_missing=false.  In
ctl_refresh() and ctl.c's arena_purge(), these calls attempted to only
refresh once, but did so in an unreliable way.
arena_i_lg_dirty_mult_ctl() was simply wrong to pass
refresh_if_missing=false.

This regression was introduced by
8d6a3e83 (Implement dynamic per arena
control over dirty page purging.).

This resolves #215.

However, unlike before it was removed do not force --enable-ivsalloc
when Darwin zone allocator integration is enabled, since the zone
allocator code uses ivsalloc() regardless of whether
malloc_usable_size() and sallocx() do.

This resolves #211.

Add mallctls:
- arenas.lg_dirty_mult is initialized via opt.lg_dirty_mult, and can be
  modified to change the initial lg_dirty_mult setting for newly created
  arenas.
- arena.<i>.lg_dirty_mult controls an individual arena's dirty page
  purging threshold, and synchronously triggers any purging that may be
  necessary to maintain the constraint.
- arena.<i>.chunk.purge allows the per arena dirty page purging function
  to be replaced.

This resolves #93.

Remove the prof_tctx_state_destroying transitory state and instead add
the tctx_uid field, so that the tuple <thr_uid, tctx_uid> uniquely
identifies a tctx.  This assures that tctx's are well ordered even when
more than two with the same thr_uid coexist.  A previous attempted fix
based on prof_tctx_state_destroying was only sufficient for protecting
against two coexisting tctx's, but it also introduced a new dumping
race.

These regressions were introduced by
602c8e09 (Implement per thread heap
profiling.) and 764b0002 (Fix a heap
profiling regression.).

Add the prof_tctx_state_destroying transitionary state to fix a race
between a thread destroying a tctx and another thread creating a new
equivalent tctx.

This regression was introduced by
602c8e09 (Implement per thread heap
profiling.).

Linux sets _POSIX_MONOTONIC_CLOCK to 0 meaning it *might* be available,
so a sysconf check is necessary at runtime with a fallback to the
mandatory CLOCK_REALTIME clock.

a14bce85 made buferror not take an error code, and make the Windows
code path for buferror use GetLastError, while the alternative code
paths used errno. Then 2a83ed02 made buferror take an error code
again, and while it changed the non-Windows code paths to use that
error code, the Windows code path was not changed accordingly.

Fix prof_tctx_comp() to incorporate tctx state into the comparison.
During a dump it is possible for both a purgatory tctx and an otherwise
equivalent nominal tctx to reside in the tree at the same time.

This regression was introduced by
602c8e09 (Implement per thread heap
profiling.).

These bugs only affected tests and debug builds.

This regression was introduced by
97c04a93 (Use first-fit rather than
first-best-fit run/chunk allocation.).

This tends to more effectively pack active memory toward low addresses.
However, additional tree searches are required in many cases, so whether
this change stands the test of time will depend on real-world
benchmarks.

Treat sizes that round down to the same size class as size-equivalent
in trees that are used to search for first best fit, so that there are
only as many "firsts" as there are size classes.  This comes closer to
the ideal of first fit.

Recent changes have improved huge allocation scalability, which removes
upward pressure to set the chunk size so large that huge allocations are
rare.  Smaller chunks are more likely to completely drain, so set the
default to the smallest size that doesn't leave excessive unusable
trailing space in chunk headers.

TlsGetValue has a semantic difference with pthread_getspecific, in that it
can return a non-error NULL value, so it always sets the LastError.
But allocator callers may not be expecting calling e.g. free() to change
the value of the last error, so preserve it.

9906660e added a --without-export configure option to avoid exporting
jemalloc symbols, but the option didn't actually work.

These regressions were introduced by
ee41ad40 (Integrate whole chunks into
unused dirty page purging machinery.).

Rename "dirty chunks" to "cached chunks", in order to avoid overloading
the term "dirty".

Fix the regression caused by 339c2b23
(Fix chunk_unmap() to propagate dirty state.), and actually address what
that change attempted, which is to only purge chunks once, and propagate
whether zeroed pages resulted into chunk_record().

Fix chunk_unmap() to propagate whether a chunk is dirty, and modify
dirty chunk purging to record this information so it can be passed to
chunk_unmap().  Since the broken version of chunk_unmap() claimed that
all chunks were clean, this resulted in potential memory corruption for
purging implementations that do not zero (e.g. MADV_FREE).

This regression was introduced by
ee41ad40 (Integrate whole chunks into
unused dirty page purging machinery.).

Extend per arena unused dirty page purging to manage unused dirty chunks
in aaddtion to unused dirty runs.  Rather than immediately unmapping
deallocated chunks (or purging them in the --disable-munmap case), store
them in a separate set of trees, chunks_[sz]ad_dirty.  Preferrentially
allocate dirty chunks.  When excessive unused dirty pages accumulate,
purge runs and chunks in ingegrated LRU order (and unmap chunks in the
--enable-munmap case).

Refactor extent_node_t to provide accessor functions.

This regression was introduced by
88fef7ce (Refactor huge_*() calls into
arena internals.), and went undetected because of the --enable-debug
regression.

This regression was introduced by
88fef7ce (Refactor huge_*() calls into
arena internals.), and went undetected because of the --enable-debug
regression.

Fix --enable-debug to actually enable debug mode.  This regression was
introduced by cbf3a6d7 (Move centralized
chunk management into arenas.).