Validator Feature - Detect infinite loop in mediation connectors

[MichielOda]

Throw a certain error when Protocol@baseFor contains the same value as Protocol/ElementType.

On older DataMiner versions this causes a crash and having a mediation connector reference its own element type is useless.

See documentation: baseFor attribute

Example of incorrect code:

<Protocol baseFor="Optical Receiver">
  <ElementType>Optical Receiver</ElementType>
</Protocol>

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