Move logic for when/how to rebind a context to a scheduler
Reintroduce correct rebibd function (not sure what happened)
Standardize on TAILQs and link for LL pointer name

Also now uses the native LL pointer in a lithe context instead of
wrapping it.
Rework logic for how libgomp lithe schedulers join
Update README to reflect true state of things
Update configure scripts for with-parlib and with-lithe
Make assertions internal so we can turn them off
Remove superfluous function declaration
Optimize do_wait for libgomp lithe with parlib

The Linux implementation of do_wait spins for a while before calling
futex_wait.  We don't need to do so because true user-level futexes are
fast.  Furthermore, if the thread that would call futex_wake were
descheduled, spinning would be disastrous.