Revert 245ae603 (Support --with-lg-page
values larger than actual page size.), because it could cause VM map
fragmentation if the kernel grows mmap()ed memory downward.

This resolves #391.

Fix mixed decl in the gettimeofday() branch of nstime_update()

This avoids bootstrapping issues for configurations that require
allocation during tsd initialization.

This resolves #390.

As a side effect this causes the extent's 'committed' flag to be
updated.

Fix a fundamental extent_split_wrapper() bug in an error path.

Fix extent_recycle() to deregister unsplittable extents before leaking
them.

Relax xallocx() test assertions so that unsplittable extents don't cause
test failures.

Deregister extents before deallocation, so that subsequent
reallocation/registration doesn't race with deregistration.

Page-align the gap, if any, and add/use extent_dalloc_gap(), which
registers the gap extent before deallocation.

Now that extents are not multiples of chunksize, it's necessary to track
pages rather than chunks.

With the removal of subchunk size class infrastructure, there are no
large size classes that are guaranteed to be re-expandable in place
unless munmap() is disabled.  Work around these legitimate failures with
rallocx() fallback calls.  If there were no test configuration for which
the xallocx() calls succeeded, it would be important to override the
extent hooks for testing purposes, but by default these tests don't use
the rallocx() fallbacks on Linux, so test coverage is still sufficient.

This facilitates the application accessing its own extent allocator
metadata during hook invocations.

This resolves #259.

rtree-based extent lookups remain more expensive than chunk-based run
lookups, but with this optimization the fast path slowdown is ~3 CPU
cycles per metadata lookup (on Intel Core i7-4980HQ), versus ~11 cycles
prior.  The path caching speedup tends to degrade gracefully unless
allocated memory is spread far apart (as is the case when using a
mixture of sbrk() and mmap()).

rallocx() for an alignment-constrained request may end up with a
smaller-than-worst-case size if in-place reallocation succeeds due to
serendipitous alignment.  In such cases, sampling may not happen.

In the case where prof_alloc_prep() is called with an over-estimate of
allocation size, and sampling doesn't end up being triggered, the tctx
must be discarded.

Rename stats.arenas.<i>.metadata.allocated mallctl to
stats.arenas.<i>.metadata .

When an allocation is large enough to trigger multiple dumps, use
modular math rather than subtraction to reset the interval counter.
Prior to this change, it was possible for a single allocation to cause
many subsequent allocations to all trigger profile dumps.

When updating usable size for a sampled object, try to cancel out
the difference between LARGE_MINCLASS and usable size from the interval
counter.

Precisely size extents for huge size classes that aren't multiples of
chunksize.