in the test that verifies key renegotiation during a large file "put", also
do a "get" of the large file (with prefetch) to verify that nothing screwy
happens.
allow prefetch + readv to occur at the same time (even though it will be really inefficient). instead of a moving pointer, use the prefetched buffers as an indication of what we've downloaded so far. break up large readv requests into the max packet size. add 2 more unit tests to test this stuff.