adding regression tests for PLs

We /really/ need to add regression tests for the PLs if it is at
all possible.

Does it make sense to sed the $with_tcl, $with_perl, and $with_python
values into the pg_regress script after modifying it to to
"createlang" the appropriate language when the corresponing with_lang
option is "yes", then add the test name to $extra_tests.

This is basically how we handle plpgsql in the tests, except that
plpgsql is not run as an $extra_test. It makes more sense to use
the $extra_tests facility for the optional PLs.

thanks.
brent

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