- always enable more compiler warnings. They are not marked as breaking
  the build anyway.

- also, always build with '--with-tests=yes'. Note that our autotools is
  actually very nice. Even if you build '--with-tests=no', you still can
  run `make check` and the tests are build on demand. The only
  difference here is whether the tests are build during `make` or during
  `make check`. While little difference, build everything during the
  `make` step.

- when running tests, use `make -k check`. Even if they fail, we want to
  run the entire test suite.

- also running tests are disabled, still run them. But don't let them
  fail the build.