Fix pagination for certain request.GET data

This didn't work at all nicely with MultiDict objects in various
circumstances and could possibly break pagination.  This fix handles
that!

This commit sponsored by Alessandro Francolini.  Thank you!

mediagoblin/tools/pagination.py

@@ -18,7 +18,7 @@ import urllib
 import copy
 from math import ceil, floor
 from itertools import izip, count
-
+from werkzeug.datastructures import MultiDict
 
 PAGINATION_DEFAULT_PER_PAGE = 30
 
@@ -98,7 +98,11 @@ class Pagination(object):
         """
         Get a page url by adding a page= parameter to the base url
         """
-        new_get_params = dict(get_params) or {}
+        if isinstance(get_params, MultiDict):
+            new_get_params = get_params.to_dict()
+        else:
+            new_get_params = dict(get_params) or {}
+
         new_get_params['page'] = page_no
         return "%s?%s" % (
             base_url, urllib.urlencode(new_get_params))