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 aq database named contrib_regression,
which is dropped and recreated at the beginhning of each pg_regress run.
This 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.

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_0_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/c8f666abde2af3060af41afe4b03ced2f62d94a9

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