a value has-a location

[Joel Brobecker]

> I intend refactoring ``struct value'' so that there is an explicit 
> location object (at present it's a union :-/).  Initially it will 
> probably remain in ``struct value''.  Once the location has been 
> separated out we can look at making it virtual with separate dwarf-2 and 
> legacy locations.

Looks good. I didn't comment on making struct value opaque, but I think
it's a terrific idea. I think we should be doing the same for struct
type, and possible struct symbol/minimal_symbol/partial_symbol as well.
And heck, we could do the same for the symtab structs as well. That
would probably help us with transforming the low/high address range
into a set of ranges, for the compilation units that are not contiguous
in memory (a long term project of mine).

-- 
Joel