Do not swallow response verification exceptions.

Fixes #571

Author: rectalogic

src/saml2/entity.py

@@ -1207,8 +1207,6 @@ def _parse_response(self, xmlstr, response_cls, service, binding,
             else:
                 response.require_signature = require_signature
                 response = response.verify(keys)
-        except Exception as err:
-            logger.error("Exception verifying assertion: %s" % err)
         else:
             assertions_are_signed = True
         finally: