Needed now that libpq.so's minor version has reached 10.

Before, make check-world would create a new temporary installation for
each test suite, which is slow and wasteful.  Instead, we now create one
test installation that is used by all test suites that are part of a
make run.

The management of the temporary installation is removed from pg_regress
and handled in the makefiles.  This allows for better control, and
unifies the code with that of test suites not run through pg_regress.

review and msvc support by Michael Paquier <michael.paquier@gmail.com>

more review by Fabien Coelho <coelho@cri.ensmp.fr>

Also add a comment about why regreesion.* aren't listed in .gitignore.

Jim Nasby

This will hopefully be easier to use than pg_config for users who are
already used to the pkg-config interface.  It also works better for
multi-arch installations.

reviewed by Tom Lane

Per request from Craig Ringer.

Noted by Radosław Smogura