Make the `.Rbuildignore` fanciness work with `set -e`.
Make the `.Rbuildignore` fanciness work with `set -e`.

I stupidly forgot that `$?` isn't something you can check with `set -e` -- if
it's on, you die before you check the previous result.

robzhu/r-travis,craigcitro/r-travis,robzhu/r-travis,eddelbuettel/r-travis,qinwf/r-travis,craigcitro/r-travis,eddelbuettel/r-travis,qinwf/r-travis,hadley/r-travis,hadley/r-travis