tests/acceptance/lib/bundles/run_ifdefined.cf: new test

Acceptance test for `run_ifdefined`.  Untested.

You need to edit the plucking rules in core.git, regenerate `plucked.cf.sub`, then do `make copy` in the `tests/acceptance` directory for this to work.  Fun.  Only then should you merge, or your acceptance tests will croak :)