subrepo: add partial diff support for git subrepos
So far, git subrepositories were silently ignored for diffs.
This patch adds support for git subrepositories,
with the remark that --include and --exclude are not supported.
If --include or --exclude are used, the subrepo is ignored.
subrepo: extend git version check to 3 digits
This allows more flexibility when a version check is required.
Some git features are introduced in a version where only
the 3rd digit changes.
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: show warning when rebase creates no changes to commit
Similar to graft:
note: rebase of 6:
eea13746799a created no changes to commit