Add support for marking failing tests as known.

To mark a failing test as a known failure, you should add a file with
a name like this:

   TESTNAME.icry.fails

When the test runs, if it fails, then the contents of this file is displayed.
It is a probably a good idea for the contents to reference the ticket where
the failure was reported.

When the problem is fixed, the `.fails` should be removed.  Failing to do
so will result in test failure (i.e., a test that passes but has a `.fails`
file is considered an error).