Fatal trap 3: breakpoint instruction fault while in kernel mode

Hi

I received a fatal trap as in the subject line during an install world. 
The system was cvsup'ed and built about six hours ago.

I hope the following (hand) transcription is helpful:

cpuid = 0; apic id = 00
instruction pointer = 0x8:0xc055125a
stack pointer = 0x10:0dabd6c3c
frame pointer = 0x10:0dabd6c3c
code segment = base 0x0, limit 0xfffff, type 0x1b
                      = DPL 0, pres 1, def32 1, gran 1
processor eflags = interrupt enabled, IOPL = 0
current process = 4 (g_down)
kernel: type 30 trap, code = 0
stopped at critical_exit+0x2a: jmp critical_exit+0x36

Trace gives:

critical_exit+0x2a
_mtx_unlock_spin_flags+0xbd
msleep+0x5d4
g_io_schedule_down+0x9f
g_down_procbody+0x48
fork_exit+0xb4
fork_trampoline+0x8
-- trap 0x1, eip=0, esp=0xdabd6d7c, ebp=0 --

Unfortunately the system is now in an inconsistent state: trying to log 
in at the prompt loops with

/libexec/ld-elf.so.1: /lib/libedit.so.4: invalid file format

Peter