Added test verifying that UNITTEST_TIME_CONSTRAINT works in TEST_FIXTURE tests.
Refactored SlowTestWithTimeExemptionPass into two tests, defined in the SlowTestHelper namespace. These tests are actually run by new test SlowTestsWithTimeExemptionsPass.
Merge pull request #26 from pjohnmeyer/fixUnitTestTimeConstraintExemptForFixtures

Fix unit test time constraint exempt for fixtures; closes #9.