Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

Check that SCM_XXX timestamp returned by the kernel is less 1 second
away in the past from the current time. This should be plenty for the
scheduler to do its job. It provides assurance that the timestamp
returned is actually a valid one, not just some random garbage.

Auto-generate 2 test cases that differ only in structure and SCM_XXX constant
used. We can do it programmatically, but that would make code convoluted
and more complex. I have two more of those types coming for the CLOCK_REALTIME
and CLOCK_MONOTONIC. This seems like an elegant and scallable approach.