Make "hg log --style=changelog > changelog" work (issue338) Style files in templates/ now take precedence over current directory. This can be overridden with --style=./changelog if really neeeded. Added test for issue338.

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