[R-gui] New Mac X11 Tcl/Tk (for R) installation method

Hi,

After a bit of discussion on the R-SIG-MAC mailing list, Stefano
Iacus has kindly provided a new method of installing X11 Tcl/Tk
for Mac OS X from a binary installer (so you don't need the
Apple Developer Tools - C compilers etc.)  Not requiring the
developer tools is obviously nice for distributing R-Tcl/Tk
GUIs to Mac "users", (rather than "developers").

See:
http://www.economia.unimi.it/R/

I think it installs X11 Tcl/Tk in /usr/local/, just as though
you had installed it from source (using the developer tools)
with the default configure prefix.  But I can't actually try
this out, because it requires administrator privileges.

For those of you who don't know the significance of this, the
native Tcl/Tk for Mac OS X is "Aqua Tcl/Tk", but R is moving
towards Aqua Tcl/Tk (from the "Unix" X11 Tcl/Tk) only gradually.
As I understand it, the standard R 1.9.1 for Mac OS X from CRAN
still expects X11 Tcl/Tk to be installed for library(tcltk) and
you certainly need X11 Tcl/Tk for tkrplot.  As far as I can
tell, before Stefano recently added this method of installing
X11 Tcl/Tk from binaries, R-Tcl/Tk "users" were expected to
install Tcl/Tk from source into /usr/local/, i.e. X11 R-Tcl/Tk
on Mac OS X has been aimed more at developers than users, while
it is still in the transition from X11 to Aqua.

I asked the R-Mac experts about the possiblity of including
Tcl/Tk binaries in $R_HOME/Tcl/ like on Windows, but that
solution isn't very nice because Mac OS X already has Tcl/Tk
(Aqua) installed automatically (in /Library/Frameworks/),
whereas there's no guarantee that a Windows user has Tcl/Tk
installed before they install R.

I don't know of any work being done to try to write an Aqua
version of tkrplot, so I'm quite happy to stick with X11
Tcl/Tk on Mac OS X for the moment, as long as my users are able
to install it.  Obviously another nice thing about X11 is that
there is plenty of Unix X11 experience in the R community.  But
I'll be quite happy to move toward the more native Aqua Tcl/Tk
in the future.

Regards,
James