* Separate build integration tests; simplify test scripts

- Move build tests out of the regular Travis unit tests, add more smoke
  test packages to build.

- Run all test scripts with bash -e, which fails on error.

- Factor coverage out into a Travis environment variable, so it's more
  obvious from .travis.yml which tests contribute to coverage and which
  don't.

- Factor dependency checking and much of the front-matter in tests
  scripts into a setup.sh script, which is sourced by all the test
  scripts.  Extra cruft in each tests script now reduced to 2 lines at
  the beginning.