LUCENE-5550: Merged revision(s) 1491222, 1491992 from lucene/dev/trunk:
- fix test to catch also NoSuchFileException
- LUCENE-5047: Handle NoSuchFileException of Java 7 like FileNotFoundException when opeining index files; document this in Directory

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1580192 13f79535-47bb-0310-9956-ffa450edef68