try to avoid install if R already installed
test
use cache to store binaries to avoid redownloading and installing from scratch each time
use cache to store binaries to avoid redownloading and installing from scratch each time
use cache to store binaries to avoid redownloading and installing from scratch each time
debugging
remove debugging; use file to store version number (can't run executable in cache as it will not work due to broken library paths)
remove stderr message for missing file
typo mdir => mkdir
add location of R to PATH so other buildpacks can have R dependencies (e.g. rpy2 will fail without this when being installed from python buildpack)
Merge pull request #7 from chahu/master

Use Cache directory & A fix to add location of R to PATH