SchemaShell --name and --file params priority fix.

Corrects the two issues identified by #4174 and CakeDC/migrations#183.

I don't currently have the proper test environment set up to run the core test suite locally, so I'm going to let Travis check things for me. I wouldn't be surprised if there is a test to fix somewhere.
Please start with capital letters in doc block "sentences" because after all they get published to http://api.cakephp.org/ and it improves readability.