Unset some local environment variables in TAP tests

Unset environment variables that control message language, so that we
can compare some program output with expected strings.  This is very
similar to what pg_regress does.

src/test/perl/TestLib.pm

@@ -39,6 +39,12 @@ BEGIN
 	  }
 }
 
+# Set to untranslated messages, to be able to compare program output
+# with expected strings.
+delete $ENV{LANGUAGE};
+delete $ENV{LC_ALL};
+$ENV{LC_MESSAGES} = 'C';
+
 delete $ENV{PGCONNECT_TIMEOUT};
 delete $ENV{PGDATA};
 delete $ENV{PGDATABASE};