templates/rss/tags.tmpl

merge: shortcircuit filemerge for identical files

- use filectx.cmp to compare files
- move merge messages into filemerge
- kill the redundant resolving message
- update tests

#header#
    <title>#repo|escape#: tags </title>
    <description>#repo|escape# tag history</description>
    #entriesnotip%tagentry#
  </channel>
</rss>