MFC r242577:

MFC r242577:
	Make OK_TO_WRITE_TO_DISK an envrionment variable instead
	of a compile time option.

	While here, don't differ based on the existence of LOCK_EX
	which doesn't seem to have ever made a difference on FreeBSD.

Approved by:	cperciva (implicit)

git-svn-id: svn://svn.freebsd.org/base/stable/9@242687 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f