regress: hfuzzraw work in progress

regress: hfuzzraw work in progress

It compiles. But:
 * close() needs to be handled specially since we are maintaining
   a synthetic fd table
 * it does not work at all yet and probably has other parts missing
 * want to (optionally) generate raw feed as part of playback
 * new fds need to get the chosen fd from the stream (and check
   it for sanity)

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>