Incorrect result for TestIntersectNull

[brynrhodes]

The TestIntersectNull test is:

Interval[1, 10] intersect Interval[5, null)

According to the spec, the expected outcome should be Interval[5, null)

However, the Java engine test suite had this expected outcome as null. In addition, there are 4 tests related to this in the published spec (TestIntersectNull1 through TestIntersectNull4) that were not in the Java engine test suite. I've added the correct expected outcome to the test suite, as well as the missing tests, but the engine now does not pass these tests (so they've been added to the skip list).