We have three temperatures, called "roof", "core", "case"
(yess rubi like word same lengt, s/he most love four).

There is a "faketemp" command that can set one two or all of them.
This allows to test negative temperatures in printouts (White Rabbit
in Siberia does it, but we southish can't test easily).

All temperatures are initialized to invalid. Example:

   wrc# faketemp -10 -2.5
   wrc# faketemp
   fff60000 fffd8003 80000000
   wrc# temp
   pcb:84.7500 roof:-10.0000 core:-2.4999 case:INVALID
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>