hash fns in order to setup conflicts.  I just removed those asserts,
so the test is not as good as it once was.

API change: rust_kernel::create_scheduler() or
rust_scheduler::rust_scheduler() respecitevly now take ownership of the
launch factory argument, it is needed to create new threads on demand.

Also renames rustrt::sched_threads() to rustrt::rust_sched_threads() for
consistency. Added rustrt::rust_max_sched_threads() to return the
maximal number of scheduled threads of the current scheduler.

Fixes #3493.

Note that the method foo.each() is not de-moded, nor the other
vec routines.

This reverts commit 1be24f07.

Not quite ready.