Add a index check function to deal with fact deleting an index fails if it doesn't exist.

thraxisp: can you review as your more familiar with why the delete index calls were needed in first place.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@5011 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9