ValidationProcessor: receive the cached processor directly from the factory

There is no point in building it into the processor itself.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Fix issue #102

As planned; create an instance of InstanceValidator for each schema/instance
validation pair and act on that.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>