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.

createlang now returns 2 for languages already exists, and regression
now allows 2 as a valid return value for createlang. Please test.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
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