graft: sort graft source revisions from lowest to highest revision number (fixes #2159)
The graft dialog is able to graft multiple revisions, and is able to graft them in a different order compared to their original order (since this is supported by the mercurial graft command itself).
However, the graft dialog is usually called by selecting multiple revisions on the repowidget. Unfortunately Qt does not always respect the order in which the items where selected on the repowidget, which makes the behavior of the graft dialog inconsistent.
To solve this issue, the repowidget will sort (from lowest to highest revision number) the source revisions before passing them to the graft dialog. Doing the sorting on the repowidget makes it possible to call the stand alone graft dialog with an unsorted list of revisions, which does work.