rationalise t/re/pat_psycho.t

rationalise t/re/pat_psycho.t

Do some cleanup of this file, without changing its functionality.

Once upon a time, the psycho tests were scattered throughout a single
pat.t file, before being moved into their own file. Now that they're all
in a single file, make the $PERL_SKIP_PSYCHO_TEST test a single "skip_all"
test at the beginning of the file, rather than testing it separately in
each code block.

Also, make some of the test descriptions more useful, and add a bit of
debugging output.