Fixing possible NoClassDefFoundError when trying to load nonexisting classes

In order to handle exceptions correctly, when classes are not found, one
needs to handle ClassNotFoundException as well as NoClassDefFoundError
in order to be sure to have caught every possible case. We did not cater
for the latter in ImmutableSettings yet.

This fix is just executing the same logic for both exceptions instead of
simply bubbling up NoClassDefFoundError.
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.
open context stats
- rename to open_contexts from open, we might have other open stats in the future related to search (lucene index searchers?)
- add a test to verify it works
Added X Versions of NGramTokenFilter and NGramTokenizer to ElasticSearch. These versions
don't produce broken positions anymore and prevent certain highlighter bugs that fail with
StringArrayOutOfBoundsExceptions as in #2931

This commit breaks backwards compatibility in terms of highlighting when NGramTokenFilter is used.
The highlighter will highlight the entire terms as produced by the tokenizer instead of the individual
sub-gram. To do sub-gram highlighting, the ngram tokenizer should be used. This behavior was based on
broken NGramTokenFilter behavior which will be fixed in Lucene 4.4 but was ported in this commit
to elasticsearch 0.90. The broken behavior can still be used if a version < LUCENE_42 is used
in the token filter mapping.

Closes #2931
Use Lucene Version that was used to create the index in Analysis
Lucene ships with a version constant that is mainly used to provide consistent behaviour across lucene release versions. Lucene's Analysis capabilities are commonly applied at index and search time such that the search-time behaviour should be identical to the index-time behaviour in most of the cases. Currently ElasticSearch always uses the latest version from Lucene which can break backwards compatibility with the index for users that rely on behaviour that changed in new Lucene version.

Users should always use the version the index was created with unless it's explicitly configured.

closes #2945
release 0.90.0 GA
move to 1.0.0.Beta1 snap
Support source include/exclude for realtime GET

Currently realtime GET does not take source includes/excludes into account.
This patch adds support for the source field mapper includes/excludes
when getting an entry from the transaction log. Even though it introduces
a slight performance penalty, it now adheres to the defined configuration
instead of returning all source data when a realtime get is done.