Bug 1085121 - Support mixed-cased (non-uppercase) doctypes. r=jrburke

propagate
https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/344
which is just propagating
https://github.com/mozilla-b2g/bleach.js/pull/9
Merge pull request #25474 from asutherland/email-mixedcase-doctypes

Bug 1085121 - Support mixed-cased (non-uppercase) doctypes. r=jrburke