Clean up the cache all functionality. We were caching false in the normal cache when a row didn't exist, but then cache all returns those rows and that causes problems elsewhere. So instead we store a separate array of rows that are found not to exist.

I also added a cache variable to store whether a cache all has been performed already.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1863 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9