Regression Test fail to run if PLPGSQL in template1

I decided to look at some system statistics (DISK IO to be specific), so I
reran the regression test on my RH5.2 box.  I was surprised when it failed
after createlang was called for plpgsql.  It should be a quick fix for Jan.
Either fix createlang to exit with a 0 status on language already installed:
143c143
<       exit 1
---
>       exit 0

Or fix it to exit with some other status and test for that status in the
Regression GNUMakefile.

Hope this helps,
	DEJ