(FACT-466) Make kernelmajversion useful in FreeBSD

FreeBSD has used a 2-element release number since before 3.0. The
current kernalmajversion returns the first two elements of
kernelversion, which is exactly the same as kernelversion on FreeBSD.
This fact now returns just the first element when on FreeBSD.
Merge branch 'pr/629' into stable

* pr/629:
  (FACT-466) Make kernelmajversion useful in FreeBSD

Closes GH-629