Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Output the diffs to standard error when comparing the expected vs the
obtained output from lastcomm instead of just printing out a summary, e.g.
"they differed".

This will make failures with results more apparent when running kyua debug,
kyua report-html, etc.

Differential Revision: https://reviews.freebsd.org/D7079 (as part of a larger diff)
MFC after: 1 week
Approved by: re (gjb)
Reviewed by: cem
Sponsored by: EMC / Isilon Storage Division

Migrate tools/regression/{usr.bin/lastcomm,usr.sbin}/ to the new tests layout.

This change was originally going to only migrate the usr.sbin tests but, as
it turns out, the usr.sbin/sa/ tests require files from usr.bin/lastcomm/
so it's better to just also migrate the latter at the same time. The other
usr.bin tests will be moved separately.

To make these tests work within the test suite, some of them have required
changes to prevent modifying the source directory and instead just rely on
the current directory for file manipulation.