* check that length is large enough to cover the non-variable part of message or
  rcom resp. (after checking that it's large enough to cover the header, of
  course).

* kill more pointless casts
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NDavid Teigland <teigland@redhat.com>