treq will silently ignore invalid non-string header values

[ryban]

If a header value is something other than a string, bytes, or list, treq will silently drop the header. It should raise an error instead.

For example this request would not send Some-Header:

treq.get('http://example.com', headers={'Some-Header': uuid.uuid4()})

This if statement needs a final else to raise an error.

treq/src/treq/client.py

Lines 171 to 175 in 7a8f45a

	if isinstance(v, (bytes, six.text_type)):
	h.addRawHeader(k, v)
	elif isinstance(v, list):
	h.setRawHeaders(k, v)

[twm]

This will no longer be silent in the next release, as treq will issue a deprecation warning. The release after that, #302 calls for a TypeError.