[RFC] New function to convert floating-point types

[Andrew Cagney]

>    Convert to DOUBLEST would just leave the format as-is.  Only when a 
>    conversion was really needed would it be converted.
> 
> Hmm.  I see DOUBLEST as a host-specific thing.  In the ideal case
> target-dependent code wouldn't need DOUBLEST at all.

The expression evaluator (used for "(gdb) print 1.0 + 2.0") is currently 
host dependant (it uses DOUBLEST) but I think it should be target dependant.

enjoy
Andrew