Don't trust the browser-provided mimetype if it looks bogus.
Review Request #6118 — Created July 19, 2014 and submitted — Latest diff uploaded
A user was reporting that their PDF file uploads were being assigned the
mimetype of "text/text/application/pdf", which is completely bogus. If
splitting on '/' produces anything other than a list of two strings, don't
allow it to proceed.
Ran unit tests.