LUCENE-5884: optimize FST.ramBytesUsed

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1617950 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5886: upgrade ecj to workaround compiler bug in precommit

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1617957 13f79535-47bb-0310-9956-ffa450edef68