mercurial/templates/atom/branchentry.tmpl

shortest: rename "test" variable to "prefix"

Sorry if this is considered churn, but "prefix" just seems much
clearer to me.

Differential Revision: https://phab.mercurial-scm.org/D3459

 <entry>
  <title>{branch|escape}</title>
  <link rel="alternate" href="{urlbase}{url|urlescape}rev/{node|short}"/>
  <id>{urlbase}{url|urlescape}#branch-{node}</id>
  <updated>{date|rfc3339date}</updated>
  <published>{date|rfc3339date}</published>
  <content type="text">{branch|strip|escape}</content>
 </entry>