When we initially created the mimetype matcher, it was okay to get some

false positives, because all it was used for was choosing an icon to

show for the file attachment. We now no longer have icons at all, but we

do have review UIs which behave completely incorrectly when there's a

bad file type. We recently added application/x-javascript to the

TextReviewUI, but this was matching all sorts of incorrect files, like

application/msdownload and application/x-pdf.
This change tightens up the scoring system a lot more, making it so that

if there aren't wildcards, both the type and subtype have to match

exactly. The addition of a vendor tag will cause the match to score

higher, but is not required.

Ran unit tests.