Add graceful fallback for invalid character encoding

[phillbaker]

For context see Pylons/webob#161

Specifically, the calls to MultiDict.from_fieldstorage end up doing a decoding and if invalid data is passed in, throw exceptions.

[bbangert]

Thanks, looks good!

[phillbaker]

Thanks @bbangert! When would this make its way into a release?

[bbangert]

@phillbaker yup, I'm writing up the changelog now actually, and will put a 2.5.0 up shortly.