Fixed #15853 - typo in m2m_changed signal documentation; thanks elbarto.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16098 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/ref/signals.txt

@@ -224,17 +224,17 @@ Arguments sent with this signal:
     This can be one of the following:
 
     ``"pre_add"``
-        Sent *before* one or more objects are added to the relation
+        Sent *before* one or more objects are added to the relation.
     ``"post_add"``
-        Sent *after* one or more objects are added to the relation
+        Sent *after* one or more objects are added to the relation.
     ``"pre_remove"``
-        Sent *after* one or more objects are removed from the relation
+        Sent *before* one or more objects are removed from the relation.
     ``"post_remove"``
-        Sent *after* one or more objects are removed from the relation
+        Sent *after* one or more objects are removed from the relation.
     ``"pre_clear"``
-        Sent *before* the relation is cleared
+        Sent *before* the relation is cleared.
     ``"post_clear"``
-        Sent *after* the relation is cleared
+        Sent *after* the relation is cleared.
 
 ``reverse``
     Indicates which side of the relation is updated (i.e., if it is the