Bug#651925: britney: refactor undo code into a method

["Adam D. Barratt" <adam@adam-barratt.org.uk>]

On Tue, 2011-12-13 at 10:03 +0100, Niels Thykier wrote:
> Attached is a patch that should do that.  I have tested it on
> the britney test suite and live data from 2011-10-19 (reduced
> to i386 and amd64).
> 
> That being said, I would appreciate a review or two just in case.

After a certain amount of munging to confirm that the two current hunks
of code are effectively identical to both each other and your proposed
new method, I've convinced myself that they are. :-)

I'd be tempted to hack on the comments a tad, but I can always do that
after it's committed if I give in...

+                single_undo = list()
+                single_undo.append((undo, item))

Any particular reason why not simply: single_undo = [(undo, item)]

+                self.undo_changes(single_undo, systems, sources, self.binaries)

I was going to grumble about this using "systems" where the existing
code always uses "self.systems", but then noticed that we do actually
declare the convenience variable already and then just never use it for
the undo code.  *mutter*

Regards,

Adam