[meld] Fix undo for grouped actions

[Kai Willadsen <kaiw src gnome org>]

commit a8a9940ff2b0c892146250244287cb3158ec3d65
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sun Jun 27 09:57:34 2010 +1000

    Fix undo for grouped actions
    
    The recent checkpoint-related undo rework requires every action to have
    an associated buffer. While this is true of all of our basic actions, it
    breaks for grouped actions. This commit adds a slightly hacky workaround
    by assuming that a group of actions all operates on the same buffer.
    While this is currently accurate, future changes could break it.

 meld/undo.py |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/meld/undo.py b/meld/undo.py
index 17569ed..31e948d 100644
--- a/meld/undo.py
+++ b/meld/undo.py
@@ -38,6 +38,9 @@ class GroupAction(object):
     """
     def __init__(self, seq):
         self.seq = seq
+        # TODO: If a GroupAction affects more than one sequence, our logic
+        # breaks. Currently, this isn't a problem.
+        self.buffer = seq.actions[0].buffer
     def undo(self):
         while self.seq.can_undo():
             self.seq.undo()