The OCLC server claims that the xml payload is encoded as latin1 (ISO-8859-1).
This causes Requests to incorrectly encode things as latin1, when actually everything is (thank goodness) UTF-8.
We can fix it by just telling Requests that it is really UTF-8
With thanks to Tex Texin, creator of http://i18nqa.com/debug/utf8-debug.html