This is a redo of r267424, which was reverted in r267432 because it broke
"make buildworld" from FreeBSD 9.x. This issue has been resolved and this
change is still "make tinderbox" clean.
This was never intended to be off by default but was done this way
because the initial patches broke the build. Things seem stable now
(have been so for a while too) and "make tinderbox" is clean so let's
try again.
Announced in freebsd-current; all reported shortcomings have been
addressed.
The description of WITH/WITHOUT tweaks should only document the non-default
option. TESTS still defaults to no, so the option to be documented is
WITH_TESTS.