Throw 411 error for unsupported data types

[SimonWoolf]

Fixes #52

[SimonWoolf]

I would like the success case first (ie string or buffer).

Done

I'm also mildly irked that the isObject() and isArray() checks each call toString() but I'll live with it.

I tried data.constructor == Object, but that kept evaluating false when run in nodeunit for, even though was true when in-browser, not sure why

[paddybyers]

but that kept evaluating false

Different contexts (eg iframes) each have a copy of these globals. The check is the correct one.

[SimonWoolf]

forgot about this pr :)

check string, then buffer, then others

nb needed to tweak isArrayBuffer to stop it erroring when fed null/undefined, if you want that check to come before the null check - 95e6a72 9decb6c