Issue 3523: Extensibility of MergeValidationException
Status:  New
Owner: ----
Reported by zigarn, Aug 18, 2015
When implementing MergeValidationListener, the only way to stop the merge is to launch a MergeValidationException.
But MergeValidationException can only work with CommitMergeStatus, which is a limited set of error causes.
It would be better to allow plugins to return other causes for not merging.