Enable MK_TESTS by default.

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.
Regen after r267424 to replace WITH_TESTS with WITHOUT_TESTS.
Avoid zeroing during allocation.

This change reverts a change from OpenBSD which made use of
calloc, and therefore wasted time initializing arrays that
will later be realloc'ed. Consistently use FreeBSD's
reallocf().

While here also merge the changes from OpenBSD's manpage
patch.1 Rev 1.27:
"patch was moved from user portability (UP) to base in issue 7
and is no longer optional"

MFC after:	1 week