Fix for #1482

[radar]

It turns out that I do know enough about the Rails process to fix this. Who would have thought?

[radar]

Oops, this fixes the controller generator but breaks the model generator in ways that I haven't yet been able to figure out. Tomorrow I will be spending the whole day driving to Brisbane so I won't be able to figure it out then.

[radar]

@josevalim: These changes add two tests for generators within an engine that are both failing, conclusively proving that it's broken within master at the moment. I have no idea myself how to fix these so any assistance I can get from either you or @drogus at understanding the generators code here would be greatly appreciated.

Per your advice, you can revert 62b207f if you wish which re-adds the engines hack that I didn't know was a hack.

[parndt]

+1 - I believe this is a blocking issue to releasing 3.1 as with this sort of functionality I believe it is incredibly important to trust that it works precisely as expected.

[drogus]

Closing as this is something that should go for #1356, I'll link it there.