Improve findoidjoins to cover more cases.

Teach the program and script to deal with OID-array referencing columns,
which we now have several of.  Also, modify the recommended usage process
to specify that the program should be run against the regression database
rather than template1.  This lets it find numerous joins that cannot be
found in template1 because the relevant catalogs are entirely empty.

Together these changes add seventeen formerly-missed cases to the oidjoins
regression test.