Fix ixallocx_prof() to clamp the extra parameter if size+extra would
overflow HUGE_MAXCLASS.

Prior to this change the debug build/test command needed to look like:

  make all tests && make check_unit && make check_integration && \
    make check_integration_prof

This is now simply:

  make check

Rename the check_stress target to stress.

arena_maxclass is no longer an appropriate name, because arenas also
manage huge allocations.

Fix xallocx() bugs related to the 'extra' parameter when specified as
non-zero.

Fix heap profiling to distinguish among otherwise identical sample sites
with interposed resets (triggered via the "prof.reset" mallctl).  This
bug could cause data structure corruption that would most likely result
in a segfault.

This resolves #269.

This didn't cause bad code generation in the one case spot-checked (gcc
4.8.1), but had the potential to to so.  This bug was introduced by
594c759f (Optimize
arena_prof_tctx_set().).

Optimize arena_prof_tctx_set() to avoid reading run metadata when
deciding whether it's actually necessary to write.

Fix TLS configuration such that it is enabled by default for platforms
on which it works correctly.  This regression was introduced by
ac5db020 (Make --enable-tls and
--enable-lazy-lock take precedence over configure.ac-hardcoded
defaults).

When junk filling is enabled, shrinking an allocation fills the bytes
that were previously allocated but now aren't. Purging the chunk before
doing that is just a waste of time.

This resolves #260.

Fix chunk purge hook calls for in-place huge shrinking reallocation to
specify the old chunk size rather than the new chunk size.  This bug
caused no correctness issues for the default chunk purge function, but
was visible to custom functions set via the "arena.<i>.chunk_hooks"
mallctl.

This resolves #264.

Fix arenas_cache_cleanup() and arena_get_hard() to handle
allocation/deallocation within the application's thread-specific data
cleanup functions even after arenas_cache is torn down.

This is a more general fix that complements
45e9f66c (Fix arenas_cache_cleanup().).

Add JEMALLOC_CXX_THROW to the memalign() function prototype, in order to
match glibc and avoid compilation errors when including both
jemalloc/jemalloc.h and malloc.h in C++ code.

This change was unintentionally omitted from
ae93d6bf (Avoid function prototype
incompatibilities.).

Fix arenas_cache_cleanup() to handle allocation/deallocation within the
application's thread-specific data cleanup functions even after
arenas_cache is torn down.

Reported by Ingvar Hagelund.

This resolves #256.

Don't bitshift by negative amounts when encoding/decoding run sizes in
chunk header maps.  This affected systems with page sizes greater than 8
KiB.

Reported by Ingvar Hagelund <ingvar@redpill-linpro.com>.

This is no longer necessary because of the more general chunk
merge/split approach to dealing with map coalescing.

Always leave decommit disabled on non-Windows systems.

Fix arena_run_split_large_helper() to treat newly committed memory as
zeroed.

This regression was introduced by
de249c86 (Arena chunk decommit cleanups
and fixes.).

This resolves #254.

Only set the unzeroed flag when initializing the entire mapbits entry,
rather than mutating just the unzeroed bit.  This simplifies the
possible mapbits state transitions.