[issue1390] Use id_t type for {get,set}priority()

[Matthew Dillon]

:The attached patch replaces `int' with `id_t' wherever appropriate. I have =
:done
:a build{world,kernel} and install{world,kernel} and I don't broke anything.=
: Plus
:some test cases I have, continue to pass.
:
:If anyone objects to this patch speak now or forever hold your peace!
:
:Cheers,
:Stathis

    I dunno.  id_t is declared in GCC's sys-types.h.  I don't see it in
    any of our own header files.  pid_t might be the better choice there,
    since pid_t is also used for things like setpgrp() and setpgid().

						-Matt