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
------
REL9_2_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/21bfc74c2743d23cf0f424bb6908e3be818ec0e8

Modified Files
--------------
doc/src/sgml/regress.sgml | 218 +++++++++++++++++++++++++++++++--------------
1 file changed, 149 insertions(+), 69 deletions(-)