Use some math tricks in arena_run_reg_dalloc() to avoid actual division, as well as avoiding a switch statement.  This change has no significant impact to performance when branch prediction is successful at predicting the sizes of objects passed to free(), but in the case that the object sizes are semi-random, this change has the potential to prevent many branch prediction misses, thus improving performance substantially.
Use some math tricks in arena_run_reg_dalloc() to avoid actual division, as
well as avoiding a switch statement.  This change has no significant impact
to performance when branch prediction is successful at predicting the sizes
of objects passed to free(), but in the case that the object sizes are
semi-random, this change has the potential to prevent many branch prediction
misses, thus improving performance substantially.

Take advantage of alignment guarantees in ipalloc(), and pad object sizes to
something less than a power of two when possible.  This has the potential
to substantially reduce internal fragmentation for objects allocated via
posix_memalign().

Avoid an unnecessary pow2_ceil() call in arena_ralloc().

Submitted by:	djam8193ah@hotmail.com

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