Merge branch 'wk/gitweb-snapshot-use-if-modified-since'

Makes 'snapshot' request to "gitweb" honor If-Modified-Since: header,
based on the commit date.

By W. Trevor King
* wk/gitweb-snapshot-use-if-modified-since:
  gitweb: add If-Modified-Since handling to git_snapshot().
  gitweb: refactor If-Modified-Since handling
  gitweb: add `status` headers to git_feed() responses.

diff --cc gitweb/gitweb.perl
Simple merge