_auto_select_degree cannot handle TensorProductElement

[Dominic Kempf]

TensorProductElement.degree returns a tuple instead of an int, but the implementation of _auto_select_degree cannot handle that. A straightforward fix would be to take the maximum of tuple entries if degree is a tuple. I can provide a PR if desired.

[Lawrence Mitchell]

FWIW, I believe that the intent is to remove the need for _auto_select_degree to exist. Since its use is in forms that use Expression without a specified degree which is deprecated.

[Miklós Homolya]

I thought I had already fixed this, no?

[Miklós Homolya]

See pull request #78.

[Dominic Kempf]

Oh boy, the introduction of max_degree made the implementation look so similar that I overlooked the fix when scanning master for a potential fix. Nevermind, thanks for fixing.

[Dominic Kempf]

implement on master (#78) already