PyMem_{Del, DEL} doesn't work yet (compilation problems).

pyport.h:  _PyMem_EXTRA is gone.

pmem.h:  Repaired comments.  PyMem_{Malloc, MALLOC} and
PyMem_{Realloc, REALLOC} now make the same x-platform guarantees when
asking for 0 bytes, and when passing a NULL pointer to the latter.

object.c:  PyMem_{Malloc, Realloc} just call their macro versions
now, since the latter take care of the x-platform 0 and NULL stuff
by themselves now.

pypcre.c, grow_stack():  So sue me.  On two lines, this called
PyMem_RESIZE to grow a "const" area.  It's not legit to realloc a
const area, so the compiler warned given the new expansion of
PyMem_RESIZE.  It would have gotten the same warning before if it
had used PyMem_Resize() instead; the older macro version, but not the
function version, silently cast away the constness.  IMO that was a wrong
thing to do, and the docs say the macro versions of PyMem_xyz are
deprecated anyway.  If somebody else is resizing const areas with the
macro spelling, they'll get a warning when they recompile now too.