String Changes for Bug 315536

[Dietrich Ayala]

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=315536
File:
http://lxr.mozilla.org/mozilla1.8/source/toolkit/locales/en-US/chrome/mozapps/downloads/unknownContentType.properties

I checked in the wrong version of the file originally, and fixed it by updating the values
yesterday. Marek brought it to my attention that this means that any localization of those strings
done between 7/14 and 7/17 is now incorrect, and that I should notify y'all here at the newsgroup.
Sorry for causing the trouble.

-d