Fixed #8867: Corrected a couple typos in the signals documentation

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8963 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/ref/signals.txt

@@ -141,7 +141,7 @@ Arguments sent with this signal:
         The model class.
 
     ``instance``
-        The actual instance being saved.
+        The actual instance being deleted.
 
 post_delete
 -----------
@@ -158,10 +158,10 @@ Arguments sent with this signal:
         The model class.
 
     ``instance``
-        The actual instance being saved.
+        The actual instance being deleted.
 
         Note that the object will no longer be in the database, so be very
-        careful what you do with this instance
+        careful what you do with this instance.
 
 class_prepared
 --------------