Break middleware into two pieces, one for request and one for response.

This allows *other* middleware that alters the /response/ based on url
information to work properly.

Added in class + DeprecationWarning for backward-compatibility.
Fix tests.
Fix tests, update docs.
Merge branch 'fix_url_quoting' into localwiki
Merge branch 'allow_url_in_response' into localwiki

Conflicts:
	django_hosts/middleware.py