Install pg_regress script to support PGXS?

[Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>]

While testing the recent pgxs patch, I noticed that you can build and
install contrib with PGXS:
	cd contrib
	gmake USE_PGXS=1 all
	gmake USE_PGXS=1 install
It seems that it ought to work to run installcheck too:
	gmake USE_PGXS=1 installcheck
but this does not quite work because the pg_regress script isn't
included in the installation tree.  (If you copy it to where it'd
need to be, installcheck works.)

Is it worth including pg_regress in the installation to make this
work?  Seems like it might be handy for external modules to be able
to run self-tests.

			regards, tom lane