Build tests on the default make target instead of 'check'.

This makes it easier to work on the unit tests since they can
be rebuilt with a simple 'make' when running them manually.
Previously one had to 'make check' to rebuild the tests, which
also runs them, making the cycle longer than necessary and
hiding any compiler warnings.
Merge pull request #62 from rillian/test-fixes-2

Build tests on the default make target instead of 'check'.