Performance improvements in SSTTest.
Performance improvements in SSTTest.

There were some stupid things, like copying large buffers for through
each callback, and less obvious issues, like seeding buffers with
random data and manually comparing the delivered data to the
source. Fixing these makes it so the test itself isn't dominating the
cost of the test anymore.

sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata