FullData: fix incomplete comment... Oops...

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

Existing code to solve issue #102 was incomplete; it failed to account for the
fact that a same instance pointer/schema URI pair may be used in a legal manner
more than once.

At the moment, yours truly only knows that the problem exists and how to solve
it, yet I fail to explain it correctly...

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Fix to issue #112 test file

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
InstanceValidator: use the new ValidationStack, fix issue #112 as a result

The code is becoming quite messy, though.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
InstanceValidator: make package private

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