stash: fix StashIndex and SaveStash

The stash command super classes needed to be updated to ContextCommand.

Closes #847
Reported-by: 林博仁 (Buo-ren Lin)
Signed-off-by: David Aguilar <davvid@gmail.com>

cola/models/stash.py

@@ -45,12 +45,6 @@ def stash_diff(self, rev):
         return diffstat + '\n\n' + diff
 
 
-class CommandMixin(object):
-
-    def is_undoable(self):
-        return False
-
-
 class ApplyStash(cmds.ContextCommand):
 
     def __init__(self, context, stash_index, index, pop):
@@ -97,7 +91,7 @@ def do(self):
                 title, 'git stash drop ' + self.stash_ref, status, out, err)
 
 
-class SaveStash(CommandMixin):
+class SaveStash(cmds.ContextCommand):
 
     def __init__(self, context, stash_name, keep_index):
         super(SaveStash, self).__init__(context)
@@ -119,7 +113,7 @@ def do(self):
                 title, 'git stash ' + cmdargs, status, out, err)
 
 
-class StashIndex(CommandMixin):
+class StashIndex(cmds.ContextCommand):
     """Stash the index away"""
 
     def __init__(self, context, stash_name):

share/doc/git-cola/relnotes.rst

@@ -70,6 +70,10 @@ Packaging
 
 Fixes
 -----
+* A regression when saving stashes was fixed.
+
+  https://github.com/git-cola/git-cola/issues/847
+
 * Diffing image files was not updating the available context menus,
   which prevented the "Stage" action from being present in the menu.