mercurial.el: ignore errors on hg-after-save-hook()
Don't signal an error even if running hg command fails. Otherwise,
succeeding hooks won't be called.
error: pretxncommit.nocommits hook failed: no commits allowed
abort: no commits allowed
transaction abort!
rollback completed
error: pretxncommit.nocommits hook failed: no commits allowed
abort: no commits allowed
transaction abort!
rollback completed