Log Message:
Fix dependency on R-Rcpp, which was moved from math/R-Rcpp to devel/R-Rcpp.

Note: this commit is part of reorganizing some of the recently
imported R packages, which are being reimported into more appropriate
categories (and removed from math) as a result of a recent discussion
on tech-pkg and privately with wiz@.  See the thread starting with:

  http://mail-index.netbsd.org/tech-pkg/2014/09/05/msg013558.html