Avoid atexit(3) when possible, disable prof_final by default.

atexit(3) can deadlock internally during its own initialization if
jemalloc calls atexit() during jemalloc initialization.  Mitigate the
impact by restructuring prof initialization to avoid calling atexit()
unless the registered function will actually dump a final heap profile.

Additionally, disable prof_final by default so that this land mine is
opt-in rather than opt-out.

This resolves #144.
Don't configure HAVE_SSE2.

Don't configure HAVE_SSE2 (on behalf of SFMT), because its dependencies
are notoriously unportable in practice.

This resolves #119.
Add configure options.

Add:
  --with-lg-page
  --with-lg-page-sizes
  --with-lg-size-class-group
  --with-lg-quantum

Get rid of STATIC_PAGE_SHIFT, in favor of directly setting LG_PAGE.

Fix various edge conditions exposed by the configure options.
Don't fetch tsd in a0{d,}alloc().

Don't fetch tsd in a0{d,}alloc(), because doing so can cause infinite
recursion on systems that require an allocated tsd wrapper.
Add AC_CACHE_CHECK() for pause instruction.

This supports cross compilation.
Add --with-lg-tiny-min, generalize --with-lg-quantum.
Remove arena_dalloc_bin_run() clean page preservation.

Remove code in arena_dalloc_bin_run() that preserved the "clean" state
of trailing clean pages by splitting them into a separate run during
deallocation.  This was a useful mechanism for reducing dirty page
churn when bin runs comprised many pages, but bin runs are now quite
small.

Remove the nextind field from arena_run_t now that it is no longer
needed, and change arena_run_t's bin field (arena_bin_t *) to binind
(index_t).  These two changes remove 8 bytes of chunk header overhead
per page, which saves 1/512 of all arena chunk memory.
Fix a prof_tctx_t/prof_tdata_t cleanup race.

Fix a prof_tctx_t/prof_tdata_t cleanup race by storing a copy of thr_uid
in prof_tctx_t, so that the associated tdata need not be present during
tctx teardown.
Add per size class huge allocation statistics.

Add per size class huge allocation statistics, and normalize various
stats:
- Change the arenas.nlruns type from size_t to unsigned.
- Add the arenas.nhchunks and arenas.hchunks.<i>.size mallctl's.
- Replace the stats.arenas.<i>.bins.<j>.allocated mallctl with
  stats.arenas.<i>.bins.<j>.curregs .
- Add the stats.arenas.<i>.hchunks.<j>.nmalloc,
  stats.arenas.<i>.hchunks.<j>.ndalloc,
  stats.arenas.<i>.hchunks.<j>.nrequests, and
  stats.arenas.<i>.hchunks.<j>.curhchunks mallctl's.
Update size class documentation.
Fix huge allocation statistics.
Fix line wrapping.