Tracing for floating point values

[Ben Elliston]

Currently, the TRACE_RESULTS web of macros/functions in
sim/common/cgen-trace.c don't know how to handle the 'f' printf-type for SF
and DF operands.  Only 'D' and 'x' are handled at present.

I set about fixing this yesterday.  There were two approaches I considered:

	* use the host's native printf %x.  Comments in sim-fpu.[hc]
	  indicate this is a bad mistake.  There's no guarantee that the
	  host will use the same floating point representation as the
	  target.

	* use sim_fpu's sim_fpu_print_fpu to output the real number
	  using cgen_trace_printf as its callback (which works nicely).
	  However, we get very detailed output!

	fr <- +1.0000,0000,0000,0000,0000,0000,0000,0000,0000,0000,0000,0000,0000,0000,0000*2^+0

Which way seems right to jump?

Ben