some packages like rgl or tcltk may need virtual framebuffers
run system2(wait = FALSE) to avoid Travis timeouts; I'll write . to stdout every 30 seconds

travis_wait is a function in the top shell environment, which is not available to R here
update branch Thu Oct  2 02:29:02 CDT 2014
update branch knitr Thu Oct  2 13:02:26 CDT 2014
update branch knitr Thu Oct  2 14:49:45 CDT 2014