Solidify the provisions for non-basic multilingual characters.

Proven successfully on the desktop browser, Nexus 7 (4.2.2) and Samsung
galaxy S3 (4.1.2), with an account with a password including spaces,
url-encoding-sensitive ascii ("&"), and a btoa-breaking multi-lingual
character from each of hebrew (" ") and chinese/japanese (" "): t &

(Note that non-basic multilinguals still break share room passwords, even
though I've wrapped that all in what should be proper provisions.  This is
fodder for a separate issue.)