If mremap(2) is available and supports MREMAP_FIXED, use it for huge
realloc().
Initialize rtree later during bootstrapping, so that --enable-debug
--enable-dss works.
Fix a minor swap_avail stats bug.
Add allocm(), rallocm(), sallocm(), and dallocm(), which are a
functional superset of malloc(), calloc(), posix_memalign(),
malloc_usable_size(), and free().
Initialize bt2cnt_tsd so that cleanup at thread exit actually happens.
Associate (prof_ctx_t *) with allocated objects, rather than
(prof_thr_cnt_t *). Each thread must always operate on its own
(prof_thr_cnt_t *), and an object may outlive the thread that allocated it.
