Fix `mongodb_user` compatibility with MongoDB 2.2 (used in Debian 7).

library/database/mongodb_user

@@ -81,11 +81,16 @@ author: Elliott Foster
 
 import ConfigParser
 try:
-    from pymongo import MongoClient
     from pymongo.errors import ConnectionFailure
     from pymongo.errors import OperationFailure
+    from pymongo import MongoClient
 except ImportError:
-    pymongo_found = False
+    try:  # for older PyMongo 2.2
+        from pymongo import Connection as MongoClient
+    except ImportError:
+        pymongo_found = False
+    else:
+        pymongo_found = True
 else:
     pymongo_found = True