Mode 1856 - Optimized indexing performance, by performing index updates only when necessary

This pull request contains the commits from https://github.com/ModeShape/modeshape/pull/753 and plus 2 additional ones:

* one which further improves performance by updating indexing only when property or path related information has changed
* one which fixes the index rebuild options in the AS7 subsystem: they were ignored up until now and the changes brought in by the previous commits exposed this