Fix memory problems in High/LowLevelBindingTests.

These tests now adaptively reduce the global work size until they
successfully allocate memory for their DirectByteBuffers. This
makes the tests work on JVMs where XX:MaxDirectMemorySize is
smaller than the modern defaults. These tests were failing on
OS X 10.6 for this reason.
Merge remote-tracking branch 'wwalker/fix_jocl_bug_981_out_of_direct_buffer_memory'