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.

Decommit arena chunk header during chunk deallocation if the rest of the
chunk is decommitted.

Cascade from decommit to purge when purging unused dirty pages, so that
it is possible to decommit cleaned memory rather than just purging.  For
non-Windows debug builds, decommit runs rather than purging them, since
this causes access of deallocated runs to segfault.

This resolves #251.

Fix arena_ralloc_large_grow() to properly account for large_pad, so that
in-place large reallocation succeeds when possible, rather than always
failing.  This regression was introduced by
8a03cf03 (Implement cache index
randomization for large allocations.)

In builds with profiling disabled (default), the opt_prof_prefix array
has a one byte length as a micro-optimization. This will cause the usage
of write in the unused profiling code to be statically detected as a
buffer overflow by Bionic's _FORTIFY_SOURCE implementation as it tries
to detect read overflows in addition to write overflows.

This works around the problem by informing the compiler that
not_reached() means code in unreachable in release builds.