Obfuscate (instead of just escape) contact/owner in gitweb summary.
This could contain an email address.
Don't let ui.username override web.contact (
issue900)
4603eef60237 introduced using ui.username before web.contact, but this was
never documented and might cause commit accidents.
- Drop web.author (deprecated since 2005)
- Try ui.username or $EMAIL as a fallback to display something useful.
- Update docs for the fallbacks.