[Rd] Patch to fix small bug in do_External and do_dotcall

[Olaf Mersmann]

I've stumbled upon a small bug/inconsitency in do_External and do_dotcall:

Here's an example:

  % LC_ALL=C R  --vanilla < symname-bug.R    

  R version 2.8.0 (2008-10-20)
  *snip*
  > options(error=expression(0))
  > ## Call 'R_GD_nullDevice' with incorrect parameter count:
  > .Call("R_GD_nullDevice", 1)
  Error in .Call("R_GD_nullDevice", 1) : 
    Incorrect number of arguments (1), expecting 0 for R_GD_nullDevice
  > 
  > ## Same call made via a NativeSymbolInfo object:
  > sym <- getDLLRegisteredRoutines("grDevices")$.Call[["R_GD_nullDevice"]]
  > .Call(sym$address, 1)
  Error: 'getEncChar' must be called on a CHARSXP

The error stems from the fact, that both do_External and do_dotcall
expect CAR(args) to be a string, while it might be a NativeSymbolInfo
object. checkValidSymbolId() already handles this, so the fix is to
use the symbol name returned from resolveNativeRoutine().

After applying the attached patch (against R-trunk revision 47348) the
output looks like this:

  % LC_ALL=C bin/R  --vanilla < symname-bug.R
  
  R version 2.9.0 Under development (unstable) (2008-12-26 r47348)
  *snip*
  > options(error=expression(0))
  > ## Call 'R_GD_nullDevice' with incorrect parameter count:
  > .Call("R_GD_nullDevice", 1)
  Error in .Call("R_GD_nullDevice", 1) : 
    Incorrect number of arguments (1), expecting 0 for R_GD_nullDevice
  > 
  > ## Same call made via a NativeSymbolInfo object:
  > sym <- getDLLRegisteredRoutines("grDevices")$.Call[["R_GD_nullDevice"]]
  > .Call(sym$address, 1)
  Error in .Call(sym$address, 1) : 
    Incorrect number of arguments (1), expecting 0 for R_GD_nullDevice

Greetings from Dortmund
Olaf