ENH: Add tests for CompositeTransformUtil tool

Two tests are added to the ANTS related to the CompositeTransformUtil tool.
The first test just makes sure that CompositeTransformUtil is run
without any failure. The second test compares the output composite
transform of the CompositeTransformUtil with a baseline composite
transform file to make sure that CompositeTransformUtil generates valid
results. To do the comparison, a new program is added to the ANTS called
"compareTwoCompositeTransforms".