Merge branch 'ct/advise-push-default' into maint

The cases "git push" fails due to non-ff can be broken into three categories; each case is given a separate advise message. By Christopher Tiwald (2) and Jeff King (1) * ct/advise-push-default: Fix httpd tests that broke when non-ff push advice changed clean up struct ref's nonfastforward field push: Provide situational hints for non-fast-forward errors