remove clause 3 from all my licenses that aren't conflicting with
another copyright claim line. again. (i did this in 2008 and then
did not update all of my personal templates.)

move stacktrace_subr() from trap.c into new mips_stacktrace.c so
it can be shared between ddb, other mips kernel components (see
locore), and an upcoming crash(8) port.

remove second copy of kdbpeek() (hidden by old DDB_TRACE
option, but they're functionally equivalent.)

tested on octeon.

ok simonb@