subrepo: move git version check into a separate method This allows checking the git version in other methods, instead of only being able to check if the version is ok or not.

rebase: show a note for updated mq patches It deserves more than a debug message. Show a note like: updating mq patch p0.patch to 5:9ecc820b1737 The message could also refer to "qrefresh" instead. Same same.

rebase: improve debug messages while processing the list of rebases

rebase: show warning when rebase creates no changes to commit Similar to graft: note: rebase of 6:eea13746799a created no changes to commit