Use duck-typing to set a quasi-integer response status.

[perey]

This change checks for integer values when setting response.status by calling int() on the supplied value, instead of explicitly checking for a subclass of int.

This is helpful to me, because I'm writing code that wraps HTTP statuses in a class that defines __int__(). I'd like to be able to use WebOb together with this class without having to check whether the Response object accepted the status, or whether I need to call int() (or str() for that matter) and try again.

This change additionally removes the need for the "if ' ' not in value" check, which assumed value was interpretable by int() anyway and then performed the same string substitution as the setter for response.status_code.

[mmerickel]

Can you please fix the failing tests.

[mmerickel]

We are losing some validation here I think.

response.status = 'InvalidStatusCodeString' will pass here and be set when it should fail, right?

[digitalresistor]

I pulled your changes, and rebased them on top of master.

[digitalresistor]

Thanks for your contribution!