Add _NEW flag to mtx(9), sx(9), rmlock(9) and rwlock(9).
A _NEW flag passed to _init_flags() to avoid check for double-init.

Differential Revision:	https://reviews.freebsd.org/D1208
Reviewed by:	jhb, wblock
MFC after:	1 Month
Fix quick_exit(3) manual page to match reality - the status was missing.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation