Rename the cv_*wait*() functions to _cv_*wait*() and change their second

Rename the cv_*wait*() functions to _cv_*wait*() and change their second
argument from a mutex to a lock_object.  Add cv_*wait*() wrapper macros
that accept either a mutex, rwlock, or sx lock as the second argument and
convert it to a lock_object and then call _cv_*wait*().  Basically, the
visible difference is that you can now use rwlocks and sx locks with
condition variables using the same API as with mutexes.