Undo history for VC revert

[Tom]

It often happens that I hack on some buffer then decide to
abandon the changes, so I vc-revert the file, but sometime later
it occurs to me the direction was correct after all and I want
the changes back.

If I decide it shortly after the revert then I may be able to get
back the changes with undo. However, if I closed the buffer since
then, or tried an other approach in the same buffer after the
revert then undo may not be available or the undo state can
diverge so much from the previously reverted version that it's
not trivial to go back to that with undo.

For this reason it would be handy if vc-revert had an undo
history. Nothing complicated, just storing the last several diffs
shown by vc-revert in memory (we don't close Emacs too often, so
it's enough) and a way to retrieve them.

This simple package does this and it's quite short and trivial,
so this feature could be added to VC as well:

http://www.emacswiki.org/emacs/VCUndoHistory