SciTools/iris — pull request #22 by bjlittle (2012-08-08 14:28:26+00:00)
Title: Automatic dimension choosing hints for merge.

Hinting is not exposed at the API level.

Fixed hint order of ```time``` over ```forecast_reference_time``` over ```forecast_period```.

Added generic framework for merge to query an ```AuxCoordFactory``` for the ```names``` of candidate ```dimensional``` coordinates that participate within the factory. It will only return coordinates that could be instantiated as a ```DimCoord```.

For the ```HybridHeightFactory``` the hint order is: ```level_height``` over ```sigma``` (```level_height``` to ```atmosphere_hybrid_height_coordinate``` naming is handled automatically).

Merge injects the PP derived ```model_level_number``` coordinate name within this hint order appropriately i.e. ```level_height``` over ```model_level_number``` over ```sigma```.

@pelson argues that by default ```model_level_number``` should be over ```level_height```.