constrain python-libmagic to at most 0.4.18. .20 breaks, .19 is not reflected at Pypi.

 - Legacy-Id: 18811

Author: rjsparks

requirements.txt

@@ -50,7 +50,7 @@ pyflakes>=1.5.0
 pyopenssl>=17.5.0		# Used by urllib3.contrib, which is used by PyQuery but not marked as a dependency
 pyquery>=1.3.0
 python-dateutil>=2.4
-python-magic>=0.4.12
+python-magic>=0.4.12,<0.4.19    # .20 is breaking, .19 is not showing on PyPi's webpage
 python-memcached>=1.56		# for django.core.cache.backends.memcached
 python-mimeparse>=1.6		# from TastyPie
 pytz>=2014.7