kernel - More threaded core dump fixes
* Try to make a more comprehensive fix for this, fixing an endless cpu
loop in the kernel in the process due to mismatched tests. Incorporate
the LWP_MP_WEXIT flag into a new test, STOPLWP().
* tsleep() is now more consistent in setting lwp_stat.
* lwpsignal() needs to allow SIGKILL through during the exit sequence
in order to wakeup any PCATCH tsleep()s.
* Fix bug in the panic coredump code where the dump_stop_usertds variable
could cause an endless tstop() loop.
Reported-by: zrj