fix commented documentation of env in sample file; add example for build matrix
Merge pull request #51 from krlmlr/env-sample

fix R_BUILD_ARGS in sample file
Cleanup sample.
Add code for dumping lots of logs.
code review comments
Merge pull request #53 from craigcitro/test_dump

Add code for dumping lots of logs.
Add qpdf in bootstrap.

Fixes #54.