At the same time we remove the "filecommand" setting, since we will
likely not have use of it thanks to PECL fileinfo.
Also the "supported" list for attachment mime types has changed
format, so we can keep track of at least some known file extensions.
Orbited plugin may not work at all anymore, I had no means to try it.
But there's a check whether 'LACONICA' is defined there, which is a
very unlikely thing in the future. So far only tests and scripts have
been migrated consistently, though.
File extensions can also be added to the upload type whitelist; they'll be normalized to types for the actual comparison, so only known extensions will work.
