* src/bddop.c, src/bddx.h, src/cache.c, src/cache.h, src/kernel.c,
src/kernel.h, src/prime.c, src/prime.h, src/reorder.c: Use power of
two for the sizes of all hash tables, in order to reduce the amount of
divisions performed.  Also allow bddhash to be smaller than bddnodes.