Should make the test more robust, we were seeing failures in the nightly builds.
When working on a new foo extension, you can now put your tests in the testsuite, set ProjectTags=-foo in mk/build.mk and skip_unless_tag('foo') in the tests.
Saves the test from failing due to small FP differences.
…istent output On some platforms $MAKE == "gmake", so the error messages still didn't match. I made it so that these tests now don't fail in make, but the exit code from GHC is emitted to stderr so we can test it.