sortIfNeeded in AbstractJoinOperation does't use the right Component reference

[hadrienk]

The sortIfNeeded() method uses the wrong reference when building the Order. This is probably dues to the expression refactoring.

The sortIfNeeded uses the component mapping (this.getComponentMapping()) to find the correct component to use for the dataset. Either the mapping is wrong (but I think I created tests for it) or the component is mutated somewhere.

[hadrienk]

I believe the problem comes from the join assignment operation. Since the assignment can change the component reference, the getData(...) method with Order parameters should be overridden.