BUG: Fix transform tests by not using dynamic_cast in vtkITKTransformConverter

This commit fixes a regression introduced
by InsightSoftwareConsortium/ITK@d1e9fe2 (BUG: Ensure Transform IO
factories are registered once.) and integrated in r24836 (ENH: Update
ITKv4 to v4.9.0 release branch).

Following this ITK commit, the ITKIO transform libraries are build as
shared and dynamic_cast can NOT be used with templated classes that are
instantiated in a translation unit different than the one where they are
defined. It will work only if the classes are explicitly instantiated
and exported.

To workaround the issue, code that was relying on dynamic_cast is updated
to (1) ensure the objects are of the right type doing string comparison
and (2) then use static_cast instead of dynamic_cast.

See InsightSoftwareConsortium/ITK@d1e9fe2
and see http://stackoverflow.com/questions/8024010/why-do-template-class-functions-have-to-be-declared-in-the-same-translation-unit

This commit fixes the following tests:
vtkSlicerTransformLogicTest1
vtkMRMLNonlinearTransformNodeTest1

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24875 3bd1e089-480b-0410-8dfb-8563597acbee