[MAT-403] Move the off-heap memory manager into OG-Maths.
[MAT-403] respond to PR comments.
[MAT-403] respond to PR comments, missed one instance.
Merge pull request #109 from OpenGamma/MAT-403

Mat 403. Add off heap memory manager.
[MAT-388] Merge stages of expression translation

Now that cleanup is handled by shared_ptr, there is no need to
separate the two stages of expression translation in to traversal
of the Java tree and construction of the RDAG tree.