catacomb/__init__.py: Awful bodge for symbol conflict.

It seems that, in Debian jessie and later, the main Python binary now
exports `md5_init' and friends.  Unfortunately, this overrides
Catacomb's existing `md5_init' with a rather different version, and the
result is a segfault (on i386) or wrong answers (on amd64).

So, as an unpleasant bodge (while this broken thing makes its way
through Debian, see bug #868366), try to force the `RTLD_DEEPBIND' flag
when loading the module.  This is unfortunate, because Python doesn't
actually advertise this flag, at least in my version.

(cherry picked from commit a3ae4a9f590ef84d8e6eac0bc94873a9fd943073)