* cleanup the template structure with hooks

* diff directory and branch support.

* distinguish different node under same path in different revisions.

* provide link with svn dav url.

* users might only be interested in the latest few active
  branches/tags - hlb
  - as well as log history. it shouldn't list all by default.

* some switches for svnweb-install to do upgrade and file merging.

* cache more branch info for performance.

* display branches only if that branch contains the current directory.

* use svn_fs_history_t to get fixed amount of log first.

* sort branch info in browse.

* supply last-modified in header and check it.
