Optional parameters are always included

[PaulWay]

There is no way to specify that an optional parameter is not supplied. This can change the test results.

For instance, a view `/songs/' might have an optional parameter 'genre'. If songs are found with that genre, then they are listed, otherwise all songs are listed. If no songs have the given genre, a 404 is returned. If oatts picks a random genre name, this most often results in a 404, which gives a false negative.

[PaulWay]

I've got a proof of concept solution for this at #14