Update stable branch to Lucene 4.9

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LUCENE-5573: Move docvalues constants and helper methods to o.a.l.index.DocValues

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LUCENE-5601: ThaiTokenizer ignores sentenceStart

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Extract the zig-zag encoding/decoding routines we have to utility methods.


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LUCENE-5602: always verify term vectors on bulk merge

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tone down TestRandomChains to avoid ngram+shingle bombs etc

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extract another zigzag encode/decode

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LUCENE-5582: remove IndexOutput.length/setLength

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SOLR-5980: AbstractFullDistribZkTestBase#compareResults always returns false for shouldFail.

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don't processEvents during rollback; prevent possible deadlock during IW.rollback

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tests: harden this test due to a current short coming in the collections api.

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LUCENE-5603: fix hunspell to use FST efficiently

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SOLR-5980: Add a test.

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merge 4.7.2 CHANGES

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LUCENE-5604: switch BytesRef/BytesRefHash hashing to MurmurHash3

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LUCENE-5604: woops, remove diagnostic conflict counter

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LUCENE-5602: CHANGES shuffle

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LUCENE-5067: add a BaseDirectoryTestCase

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LUCENE-5067: fix testThreadSafety to actually test the dir in question (not copy into random impl), fix performance issues, remove Nightly

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LUCENE-5067: add more tests

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