[c-run-time] MMAllocMisc/MMAllocFree uses unsigned long to match generated code.
[c-ffi,dfmc] Added [s]size_t support as raw-c-[s]size-t
[common-dylan,system] Made some FFI functions use correct [s]size_t signatures.
[c-ffi] Added a few unit tests for size_t/ssize_t.