JENA-567 Add option to TDB for specifying where the temporary write blocks for the BlockMgrJournal come from.  Also added a memory mapped ByteBuffer allocator to work with the new BlockMgrJournal functionality.

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1535599 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch: upstream/trunk