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.
adding a
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
a renamed from b:9a263dd772e0159ddfa70fb8a448bb6c7ec8c69f
% test with --rev
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3