[$] Capability analysis for the kernel

One of the advantages of the Rust type system is its ability to encapsulaterequirements about the state of the program in the type system;often, this state includes which locks must be held to be able to carry outspecific operations. Clacks the ability to express theserequirements, but there would be obvious benefits if that kind of featurecould be grafted onto the language. The Clang compiler has made somestrides in that direction with its thread-safetyanalysis feature; two developers have been independently working totake advantage of that work for the kernel.