subrepo: print paths relative to upper repo root for push/pull/commit
This makes more sense when using multiple levels of
nesting.
This happens to help a lot in a case where 3 projects
of mine all use the same makefile helper project as a
sub. A fourth project use these first three projects
and current output made it very hard to figure
which makefile helper was committed. it looked more
like the project was committed/pushed/pulled three times
in a row than dealing on three different repos.