Merge branch 'jn/gitweb-side-by-side-diff'

* jn/gitweb-side-by-side-diff:
  gitweb: Add navigation to select side-by-side diff
  gitweb: Use href(-replay=>1,...) for formats links in "commitdiff"
  t9500: Add basic sanity tests for side-by-side diff in gitweb
  t9500: Add test for handling incomplete lines in diff by gitweb
  gitweb: Give side-by-side diff extra CSS styling
  gitweb: Add a feature to show side-by-side diff
  gitweb: Extract formatting of diff chunk header
  gitweb: Refactor diff body line classification