Add assert that fails one Elasticsearch upgrades to Lucene 4.3 in order to remove the duplicated class
Added temporary fix for LUCENE-4899 where FastVectorHighlihgter failed with StringIndexOutOfBoundsException
if a single highlight phrase or term was greater than the fragCharSize producing negative string offsets

The fixed BaseFragListBuilder was added as XSimpleFragListBuilder which triggers an assert once Elasticsearch
upgrades to Lucene 4.3
Remove XSimpleFragmentsBuilder and XScoreOrderFragmentsBuilder since the only difference
to the lucene version is that `discreteMultiValueHighlighting` does default to `true`. Yet
we set this anyway in the HighlightingPhase such that the classes are obsolet.