check null or exists before deleting file

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1593884 13f79535-47bb-0310-9956-ffa450edef68
add assert to maybe trick G1GC into not doing this (or at least make the fail explicit)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1593971 13f79535-47bb-0310-9956-ffa450edef68
fix rare test fail

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1593976 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5668: fix ob1 in TieredMergePolicy

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1594059 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5668: er, actually fix the bug

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1594096 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5668: fix the codec so segment sizes don't change on each flush

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1594107 13f79535-47bb-0310-9956-ffa450edef68