ttymsg: Create ttymsgat()

[jfree]

Summary

Unlike ttymsg(), ttymsgat() does not attempt to open a device. It will
send its message to the device represented by the by the fd argument.

The ttymsg() function now opens the provided device and passes it into
ttymsgat() for processing.

[markj]

usr.bin/wall/ttymsg.c

76

Please try to avoid mixing style changes with functional ones.

109

You might also check that the fd is non-blocking, since this code assumes that it is. fcntl(fd, F_GETFL) should tell you.

[jfree]

• Remove style(9) changes
• Check for blocking fd

[markj]

usr.bin/wall/ttymsg.c

176

There's no real purpose in closing an fd right before exiting, I wouldn't bother with it.