Bug in computing max profit over all forms

[hanase]

There is the same bug as in the public version of the model: When passing all forms (i.e. forms=None) into the developer model, the max profit is not computed. It's in _get_dataframe_of_buildings.

I submitted a PR fix for the previous version a while ago (still open):
UDST/urbansim#194

I probably cannot do a PR on a private repository without forking it to a public repository, so I won't.

[pksohn]

Thanks Hana. I'll mimic the change from the PR on urbansim.

FYI, as far as I know, forking a private repo remains private by default in GitHub, and doesn't count against any kind of private repo quota: https://help.github.com/articles/about-forks/.

[hanase]

Thanks Paul! Good to know about the forking!