LUCENE-5969: make branch for the heavy parts

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627530 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969, LUCENE-5412: make .si immutable again, and make ancient writers read-only

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627535 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: file mismatch detection for 5.0 fnm

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627544 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: add AssertingLiveDocsFormat

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627564 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: improve checks for livedocs

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627593 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: beef up AssertingLiveDocs more

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627669 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: take bitvector out back and shoot it

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627701 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969, LUCENE-5895: fix sign bit bugs in segment/commit IDs, use byte[] representation

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627714 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: add remaining infos/deletions safety

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627805 13f79535-47bb-0310-9956-ffa450edef68
merge trunk

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1627806 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969, LUCENE-5412: add more infos/metadata safety

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1627941 13f79535-47bb-0310-9956-ffa450edef68