Bill's ndindex stuff

Replaces https://github.com/cpelley/iris/pull/13

Issue with results that changes due to @bjlittle's changes (not due to merging in these changes).

Tests extended to indicate the issue at hand.  These will need fixing at a later stage.
**1.  lib/iris/tests/test_interpolation.py TestNearestLinearInterpolRealData.test_circular**
**2.  lib/iris/tests/test_trajectory.py TestTrajectory.test_trajectory_extraction**