Add the `osx` branch to those tracked by the build shield.
Add a short note to a weird line in `.travis.yml`.

[skip ci]
test code for r_install
vectorized RInstall
apt-get update only once should be enough
do not install littler for now (for lack of /usr/bin/r on OS X)
make devtools installation optional yet automatic for the two functions using devtools
Merge pull request #30 from eddelbuettel/master

do not install littler for now and make devtools optional
Get pedantic about variable names.
Merge pull request #28 from krlmlr/nitpick

Nitpicking
Trivial cleanups after Kirill's fixes.
Re-add Kirill's cleverness with testing.
add travis-tool.sh to package's .Rbuildignore during bootstrap

The name of the travis-tool.sh script should be opaque to the user,
and the script is not even part of the package repository.
set CRAN URL via environment variable RTRAVIS_CRAN_URL, default http://cran.rstudio.com

An "options" call is appended to `Rprofile.site` during bootstrapping
Merge pull request #33 from krlmlr/rbuildignore

add travis-tool.sh to package's .Rbuildignore during bootstrap
Merge pull request #32 from krlmlr/6-cran-url

set CRAN URL via environment variable RTRAVIS_CRAN_URL, default http://cran.rstudio.com
Merge branch 'master' into osx

Conflicts:
	.travis.yml