Patch by Ax to fixe and improve to the core doxygen PHPdoc:

  * fixes all doxygen warnings [#]_ in the current code base
    + changes @param style from phpDocumentor (@param type $var desc) to doxygen (@param $var desc)
    + documents all undocumented parameters
    + escapes / fixes html warnings
    + fixes @defgroup in theme.inc
  * adds more groupings [#]_
    + drupal_{set|get}_title, drupal_{set|get}_breadcrumb
    + pager.inc: pager_api (pager_query(), pager_display()), pager pieces
  * adds a new group "themeable" which contains all themeable functions.