backport executeAudited()
use executeAudited() for all cache queries

Conflicts:
	lib/files/cache/cache.php
remove leftover execute() and unused  variables
adding second argument to DatabaseException
updated some PHPDoc comments
fixing undefined variable in line 789 - actually unrelated but well ....
Merge pull request #5640 from owncloud/backport_executeaudited_stable5

Backport executeaudited stable5