[library, tests] Added simple Treap library that is non-parametric in
the hopes of shaking out a bunch of lingering compiler bugs. This
required adding randomness to CompilerBuiltin (where it _doesn't_
disrupt testing times). Right now Treap doesn't even pass type
checking yet due to #360. Coalescing Treap and TreapTest into a
single file turns up code generation bugs having to do with the
internals of asm; the ManglingClassWriter has been modified to give
more information about these sorts of failure in the hopes that we can
debug the problems in future.
