pep8
- pep8
 - removed mutable default values
 - foo == None -> foo is None
fix removed api change regarding spectral functions
Merge pull request #2514 from tacaswell/mpl_toolkit_pep8

Mpl toolkit pep8
Merge pull request #2547 from toddrjen/apideltafix

fix removed api change regarding spectral functions
re-ordered the list of artists returned by
`legend_handler.HandlerErrorbar`
pep8 fixes