[Rd] Avoid texinfo 6.1

[Prof Brian Ripley]

There are problems with the texi2dvi in the recently released texinfo 
6.1.  (The bug has been reported.)  Avoid 6.1 if you can, but if not 
setting the environment variable

R_TEXI2DVICMD=emulation

will enable R to build, including NEWS.pdf and all the vignettes.

We are working on a more complete workaround for R-devel and 3.2.4.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Emeritus Professor of Applied Statistics, University of Oxford