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.
abort: repository a not found!
255
abort: error: Connection refused
255
abort: repository a not found!
255
abort: destination '../a' already exists
255
abort: repository a not found!
255
destination directory: q
abort: destination 'q' already exists