which will stack allocate small (128 or less bytes) blocks and Malloc the
rest...naturally these now have to be paired with __PHYSFS_smallFree() calls,
so you can't be as lazy as a basic alloca() would let you be. The benefit is
both less malloc pressure for those temporary allocations and better stack
overflow safety (so if some jerk tries to push a 78 megabyte string through
the library as a filename, we won't try to strcpy it to the stack).