LUCENE-5164: Fix default chunk sizes in FSDirectory to not be unnecessarily large (now 8192 bytes); also use chunking when writing to index files. FSDirectory#setReadChunkSize() is now deprecated and will be removed in Lucene 5.0

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1512937 13f79535-47bb-0310-9956-ffa450edef68