Provide FreeDOS test kernel builds

[boeckmann]

I would like to provide recent binaries of the FreeDOS kernel Git master branch in form of an additional package, named probably FDTKERN.

[mateuszviste]

Sounds good. A different approach would be to add such "unstable" builds as alternative versions to the current package. But then the version string would need to be manipulated so it sorts lower than the current stable, otherwise it would be proposed to users as the default.