MFC r273129:
Implement FIODTYPE for master ptys.
MFC r273130:
Change the deadfs poll VOP to return POLLIN|POLLRDNORM if the caller
is interested in i/o state.  Return POLLNVAL for invalid bits, similar
to poll_no_poll().
MFC r273131:
When vnode bypass cannot be performed on the cdev file descriptor for
read/write/poll/ioctl, call standard vnode filedescriptor fop.
MFC r273132:
Style changes for deadfs.