[Groff] inconsistency between .R and \*R in man.tmac

[Bernd Warken]

groff_man(7) states

       .R [text]
              Causes text to appear in roman font.  If no text is
              present on the line where the macro is called, then
              the  text  of the next line appears in roman.  This
              is the default font to which text  is  returned  at
              the end of processing of the other macros.

       \*R    The `registered' sign.


As macros and strings share the same name space this isn't consistent.
The tmac source implements the string variant.  man(7) does not have 
either of them.  

Maybe the documentation of .R should just removed from groff_man(7).
That's not too great a loss because the funtionality of .R can be
achieved by calling .RI with a single argument:

.RI "This is all in roman font."

Bernd Warken