python-werkzeug: needs python zlib support

Otherwise import fails:

>>> import werkzeug
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/site-packages/werkzeug/__init__.py", line 154, in <module>
  File "/usr/lib/python2.7/site-packages/werkzeug/exceptions.py", line 71, in <module>
  File "/usr/lib/python2.7/site-packages/werkzeug/wrappers.py", line 35, in <module>
  File "/usr/lib/python2.7/site-packages/werkzeug/formparser.py", line 21, in <module>
  File "/usr/lib/python2.7/site-packages/werkzeug/wsgi.py", line 17, in <module>
ImportError: No module named zlib

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>