Fix some tests.

These tests previously relied on testthat quietly ignoring additional entries
in the `regexp` for `expect_error`; the version on github checks that, so
these tests are now failing. I fixed them by making the regexps a little
uglier; feel free to tell me to think harder about it. ;)
Merge pull request #48 from craigcitro/fixtests

Fix some tests.
Merge branch 'master' into travis