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.
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b