R_xxx counterparts to the V_xxx macros

[James Gritton]

There are places where a variable has been replaced with a V_ macro, 
only to be set explicitly to the "virtual" data from thread0 or the 
like.  For example, I know of a few places where V_hostname is set like 
this.

It would make sense to have an R_hostname as well, an easy shortcut the 
the real hostname instead of the virtual one.  You'd need either a 
static "vprocg0" structure, or a pointer somewhere to the main entry 
(could be thread0 again, I suppose).  Likewise with the other structures 
where other globals may live.

Perhaps many (most?) variables will only ever be referred to in their 
fully virtual state.  But for those where the intention is to use the 
machine's "true" parameter, it would be more clear if that was made 
explicit in the macro.

- Jamie