Merge pull request #905 from pfalcon/remove-zlibd

Remove zlibd, superceded by uzlib
modure: Update to re1.5 v0.6, support for char sets/classes ([a-c]).
py: Fix dummy definition of BEGIN/END_ATOMIC_SECTION.
py: Fix GC realloc issue, where memory chunks were never shrunk.

Previously, a realloc to a smaller memory chunk size would not free the
unused blocks in the tail of the chunk.