For some experiments I wanted to run the regression tests using a different
database (possibly using pg_regress --dbname=), but the name "regression" is
hardcoded in a few places. It's trivial to fix, see attached patch. Quick
explanation: The fact that psql's \z prints the database name has always been
an inconsistency, so it's good to get rid of anyway. The majority of the
diff in prepare.out is whitespace differences. Objections?
