diff -r fd6e9c7cd98c -r e451e599fbcf mercurial/mdiff.py
--- a/mercurial/mdiff.py	Fri Jan 01 20:52:05 2010 +0100
+++ b/mercurial/mdiff.py	Fri Jan 01 20:54:05 2010 +0100
@@ -27,7 +27,9 @@
     nodates removes dates from diff headers
     ignorews ignores all whitespace changes in the diff
     ignorewsamount ignores changes in the amount of whitespace
-    ignoreblanklines ignores changes whose lines are all blank'''
+    ignoreblanklines ignores changes whose lines are all blank
+    upgrade generates git diffs to avoid data loss
+    '''
 
     defaults = {
         'context': 3,
@@ -38,6 +40,7 @@
         'ignorews': False,
         'ignorewsamount': False,
         'ignoreblanklines': False,
+        'upgrade': False,
         }
 
     __slots__ = defaults.keys()