ENH: Disallow vector multiply by itself

Problem detected by erroneous programming; using MultiplyImageFilter
with VectorImage with all three template parameters got into a
situation where the template function operator* called
itself, causing unbounded recursion.

Change-Id: Ie38ad4f508d2055b0fe9baa160d066145f20245d
Merge topic 'VECTOR_UNBOUNDED_RECURSION'

770fe1a4 ENH: Disallow vector multiply by itself