* rename private functions to use underscore
* rename some public functions to match the usual style
* adjust pdf/ preview driver to use the renamed functions
* we where leaking a single message in _ConstructGui, otherwise no functional change
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@26396 a95241bf-73f2-0310-859d-f6bbb57e9c96