Update src/2013-01-16-timing-normal-rngs.Rmd

Add variant of the std designation for (I think) some earlier versions of compilers (g++ < 4.7)
Merge pull request #14 from etiennebr/patch-1

Indeed -- the same is true for the two C++11 articles.  "Soon" Rcpp will have proper plugin support and we'll add a plugin for C++11 which should know how to fall back to =std=c++0x.  Thanks!