[patch] Require _KERNEL/_KERNEL_STRUCTURES for all kernel headers

[Matthew Dillon]

:- sys/xwait.h can be removed, if Matt doesn't want to resurrect it. It's
:  only used by kern/kern_sync.c and there only by #if 0'd code.
:
:Joerg

    Yah. sys/xwait.h can go.

					-Matt
					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>