panic on HEAD

[Matthew Dillon]

:After a week of uptime:
:
:panic: assertion: tok->t_cpu == gd in lwkt_reltoken
:panic messages:
:---
:panic: assertion: tok->t_cpu == gd in lwkt_reltoken
:mp_lock = 00000000; cpuid = 0; lapic.id = 00000000
:boot() called on cpu#0
:Uptime: 7d1h48m15s
:
:dumping to dev #da/0x20001, offset 378927
    
    I suggest running a kernel with KTR logging compiled in:

    options         KTR
    options         KTR_ALL

    Then if it happens again I'll have a tracelog of all operations
    that were made on the token involved.

    I think this is another race in lwkt_switch() due to lwkt_switch()
    trying to manipulate the tokens for a thread other then the current
    thread.  Man, this is turning out to be a lot more finicky then I 
    would like!

    The core you uploaded looks good.  I'm investigating it now but I
    may not have enough information to locate the bug without a KTR log.

						-Matt