add ignore for backward-codecs intellij module file

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1627186 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5569: *AtomicReader/AtomicReaderContext have been renamed to *LeafReader/LeafReaderContext (merged 1627178)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1627188 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: Add Lucene50Codec (infos, dv, norms)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1627189 13f79535-47bb-0310-9956-ffa450edef68