Use vn_io_fault for the writes from core dumping code.  Recursing into
VM due to copyin(9) faulting while VFS locks are held is
deadlock-prone there in the same way as for the write(2) syscall.

Reported and tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Fix some cosmetic issues with the use of kmem_malloc() in the i386 LDT
sysarch(2) code.

Use M_ZERO instead of explicit bzero(9).  Do not check for failed
allocation when M_WAITOK is specified (which is specified always).
Use malloc(9) when allocating memory for the intermediate copy of the
user-supplied buffer.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Fix two issues:

 - Check for rc.d directory's existence before traversing
   it;
 - Don't output * when rc.d directory is empty.

PR:		conf/190665
Submitted by:	Oleg Ginzburg <olevole olevole ru> (with changes)
MFC after:	2 weeks