LUCENE-4995: Don't hold references on large decompression buffers in CompressingStoredFieldsReader (merged from r1491374).

CompressingStoredFieldsReader now only reuses an internal buffer when there is
no more than 32kb to decompress. For large blocks, a dedicated decompression
buffer will be created on demand.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1491378 13f79535-47bb-0310-9956-ffa450edef68