cmdutil.commit: use relative paths in the error messages
This is more consistent with other error messages and requires
less makeup in test-commit and test-symlink-basic.
error: pretxncommit.nocommits hook failed: no commits allowed
transaction abort!
rollback completed
abort: no commits allowed
error: pretxncommit.nocommits hook failed: no commits allowed
transaction abort!
rollback completed
abort: no commits allowed