Stephen Rothwell <sfr@canb.auug.org.au>: fix for sigio delivery:
  Hi Linus,

  This patch means that we keep the upper 16 bits of the si_code
  field of the siginfo structure that is delivered with and SIGIOs.
  We need this so that the code that actually copies the siginfo_t
  out to user mode knows which part of the union to copy.  We currently
  get away with out this information because we always copy at least
  two ints worth of the union, but this s an ugly hack and I would
  like to tidy it up.

  Comments?