Add PoC JetBrains Xodus backend.

http://jetbrains.github.io/xodus/


git-svn-id: https://svn.forgerock.org/opendj/trunk@11398 41b1ffd8-f28e-4786-ab96-9950f0a78031
Fumble about in the dark a bit trying to improve the tuning. These settings increased read/write throughput for me by about 20-25%, but the log cleaning still does not keep up.

git-svn-id: https://svn.forgerock.org/opendj/trunk@11400 41b1ffd8-f28e-4786-ab96-9950f0a78031