Merge branch 'jn/gitweb-blame' (early part)

* 'jn/gitweb-blame' (early part): gitweb: Use light/dark for class names also in 'blame' view gitweb: Add author initials in 'blame' view, a la "git gui blame" gitweb: Mark commits with no "previous" in 'blame' view gitweb: Use "previous" header of git-blame -p in 'blame' view gitweb: Mark boundary commits in 'blame' view gitweb: Make .error style generic