cache issue

[John Keeping]

On Tue, Mar 03, 2015 at 11:56:11PM +0100, Jason A. Donenfeld wrote:
> Thanks! Merged. It would be nice to see a test case built out of the
> example you gave in the commit message.

It has to run for a couple of minutes to get sensible results.  I guess
we could introduce an EXPENSIVE prerequisite in the same way Git does,
but I'm not sure how often anyone would run the test suite with that
turned on.