Enabling batch support for indexes + bug fixes.

Now we correctly handle batches of updates - all updates for a given row are grouped into
a single Index Batch which is then processed by the usual update mechanisms.

Other Bug Fixes:
 - Wrong ordering in MutableIndexTest
 - Wasn't setting pending updates before cleanup
 - Adding debugging statements (and toString impls)
 - Removing ColumnFamilyIndexer since its a worse example than the CoveredColumn or Phoenix indexer
 - making stopped AtmoicBoolean in IndexWriter to help race conditions in stop/write
 -- might be cause of the concurrent modification issue when HRegion#doClose seen sometimes in the test.