rebase: provide detailed hint to abort message if working dir is not clean
Detailed hint message is now provided when 'pull --rebase' operation detects
unclean working dir, for example:
abort: uncommitted changes
(cannot pull with rebase: please commit or shelve your changes first)
Added tests for uncommitted merge, and for subrepo support verifying that same
hint is also passed to subrepo state check.
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..