clean stack trace code.

clean stack trace code.
format is unchanged but shows all frames
(old loop stopped one frame early).

wreck=; 6.out
cannot convert type *main.S·interface2 to interface main.I·interface2: missing method Foo
throw: interface conversion
SIGSEGV: segmentation violation
Faulting address: 0x0
pc: 0x256d

throw+0x46 /home/rsc/go/src/runtime/runtime.c:68
	throw(0x863a, 0x0)
hashmap+0x188 /home/rsc/go/src/runtime/iface.c:167
	hashmap(0x8760, 0x0, 0x85b0, 0x0, 0x0, ...)
sys·ifaceT2I+0xa8 /home/rsc/go/src/runtime/iface.c:201
	sys·ifaceT2I(0x8760, 0x0, 0x85b0, 0x0, 0x0, ...)
main·main+0x4e /home/rsc/go/src/runtime/rt0_amd64_darwin.s:87
	main·main()
mainstart+0xf /home/rsc/go/src/runtime/rt0_amd64.s:70
	mainstart()
sys·goexit /home/rsc/go/src/runtime/proc.c:110
	sys·goexit()

R=r
DELTA=44  (5 added, 15 deleted, 24 changed)
OCL=20358
CL=20368