jemalloc is configured.

Modify arena_malloc() API to avoid unnecessary choose_arena() calls.  Remove
unnecessary code from choose_arena().

Enable lazy-lock by default, now that choose_arena() is both faster and out of
the critical path.

Implement objdir support in the build system.

Implement minimal Makefile.

Make compile-time-optional jemalloc features controllable via configure
options (debug, stats, tiny, mag, balance, dss).

Conditionally exclude most of the opt_* run-time options, based on configure
options (fill, xmalloc, sysv).

Implement optional --enable-dynamic-page-shift.

Implement optional --enable-lazy-lock.

Re-order malloc_init_hard() and use the malloc_initializer variable to support
recursive allocation in malloc_ncpus().

Add mag_rack_tsd in order to receive notifications of thread termination.

Add jemalloc.h.