[seL4] Tidying and real-time

This commit… https://github.com/seL4/seL4/commit/c5b6a6a58aae75129cdf5a83f861bdacddbf51d6 … is pleasing. As is the RT API. Passive servers! A seemingly viable and sensible approach to user-space scheduling! Just a quick thumbs up for recent progress. :-)