pgsql: Update regression testing instructions.

Update regression testing instructions.

This documentation never got the word about the existence of check-world or
installcheck-world.  Revise to recommend use of those, and document all the
subsidiary test suites.  Do some minor wordsmithing elsewhere, too.

In passing, remove markup related to generation of plain-text regression
test instructions, since we don't do that anymore.

Back-patch to 9.1 where check-world was added.  (installcheck-world exists
in 9.0; but since check-world doesn't, this patch would need additional
work to cover that branch, and it doesn't seem worth the effort.)

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/bfd59426db52b934a3883c7d3a27b2ce8798afe5

Modified Files
--------------
doc/src/sgml/regress.sgml |  209 ++++++++++++++++++++++++++++++---------------
1 file changed, 139 insertions(+), 70 deletions(-)