pgsql: Add mode where contrib installcheck runs each module in a separa

Add mode where contrib installcheck runs each module in a separately named database.

Normally each module is tested in a database named contrib_regression,
which is dropped and recreated at the beginhning of each pg_regress run.
This new mode, enabled by adding USE_MODULE_DB=1 to the make command
line, runs most modules in a database with the module name embedded in
it.

This will make testing pg_upgrade on clusters with the contrib modules
a lot easier.

Second attempt at this, this time accomodating make versions older
than 3.82.

Still to be done: adapt to the MSVC build system.

Backpatch to 9.0, which is the earliest version it is reasonably
possible to test upgrading from.

Branch
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/5dd1c287c2866213a753495551dd75d9c18edbcb

Modified Files
--------------
contrib/dblink/Makefile | 3 +++
src/Makefile.global.in | 9 +++++++++
src/makefiles/pgxs.mk | 6 +++++-
3 files changed, 17 insertions(+), 1 deletions(-)