MODE-2124 Changed the code so that child node re-indexing (on update of the parent) is only performed when the path of the parent has changed. 

Also, based on additional CPU usage profiling, removed a `String.intern` call.

@rhauch: after fixing the indexing issue, additional profiling showed a significant hot-spot in an `intern` call

![profiling_hotspot](https://f.cloud.github.com/assets/995683/1806139/c90ab39c-6ca3-11e3-9ac5-4e8c0b6461c0.png)

Some additional links regarding the benefits/drawbacks of intern: http://hype-free.blogspot.ro/2010/03/stringintern-there-are-better-ways.html & http://www.codeinstructions.com/2009/01/busting-javalangstringintern-myths.html