fix bug 928302, 929373, 931412 - Check if the search index entry of a wiki document should really be updated during saving or deleting.

This fixes the problem of accidentally indexing wiki documents which  
aren't supposed to be index when saving or deleting them.
Merge pull request #1631 from jezdez/improved-indexables-928302

fix bug 928302, 929373, 931412 - Check if the search index entry of a wiki document should really be updated during saving or deleting.