set the pipefail option, otherwise `foo | tee`'s status code will be 0 (success) even if foo failed

accordingly, must use bash instead of the default sh
make it possible to check package rev deps by writing [crandalf ???@user/repo] in the commit message, where ??? is the package name, and you can optionally specify the github repo

for example, let's see if it works with [crandalf highr@yihui/highr]
add a recipe for Rglpk
need to keep n

[crandalf highr@yihui/highr]
don't try to attach packages in the current R session, because it will be very difficult to cleanly detach the package

e.g. we might get erros like this even if the package is loadable

Error in dyn.load(file, DLLpath = DLLpath, ...) :
  unable to load shared object '/home/travis/R/goftest/libs/goftest.so':
  `maximal number of DLLs reached...
see if I can suppress the messages of the form

Creating config file /etc/texmf/texmf.d/05TeXMF.cnf with new version
more jobs in the knitr matrix
yihui updated branch pkg/knitr Sat Oct  4 17:38:22 CDT 2014
yihui updated branch pkg/knitr Sun Oct  5 11:38:48 CDT 2014
yihui updated branch pkg/knitr Sun Oct  5 12:15:38 CDT 2014
yihui updated branch pkg/knitr Mon Oct  6 01:05:24 CDT 2014