Fixes a bunch of warnings like
htmlparse.y:509:25: warning: operation on ‘self->userData->buf’ may be undefined [-Wsequence-point]
htmlparse.y:518:29: warning: operation on ‘self->userData->tmp_buf’ may be undefined [-Wsequence-point]
which were a result of (macro-expanded) code like this (simplified):
if ((tmp = (tmp = PyMem_Realloc(...))) == NULL) return NULL;
The PyMem_Resize(p, ...) macro assigns the new value to p before
returning it, so there's no need to assign it again.
See http://bugs.python.org/issue1668036 for evidence (from 2007) that
this is indeed a documented side-effect of the macro API.
