Fix issue in xd3_encode_memory causing error when IOPT buffer capacity reached and a copy reaches the end-of-source, causing unexpected request for second source block. New tests to cover this case. Removed the IOPT limit in xd3_encode_memory (improves compression).  Doubles sizing of the large-checksum hash table (fewer collisions, better compression).

git-svn-id: http://xdelta.googlecode.com/svn/trunk@406 a3eca27d-f21b-0410-9b4a-6511e771f64e