- Fix UTF-8 regression test when running with LC_{CTYPE,ALL}=C by setting
LC_ALL to UTF-8.
- Add explicit regression test for when locale C

Found the hard way by tb@.
input and OK on earlier version

- Fix UTF-8 regression test when running with LC_{CTYPE,ALL}=C by setting
LC_ALL to UTF-8.
- Add explicit regression test for when locale C

Found the hard way by tb@.
input and OK on earlier version bluhm@

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Regression test for UTF-8 separator for join(1).

Add regression test for joining on NULL columns.

Enable regress tests testing the bugs reported in
https://marc.info/?l=openbsd-bugs&m=153885229604587&w=2
and http://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=1356 as well

Basic set of tests taken from spec plus some extra. Extra ones are failing
and disabled for the moment.