Preserve full load/exec for untyped files and use MimeMap
- Rather than turning any untyped file into ",lxa" suffix and losing the load/exec address, append ",llllllll-xxxxxxxx"
- Suffixes format is compatible with HostFS (RPCEmu et al), so viewing an emulator's directory preserves them
- Reading an ",lxa" behaves as before, but they are no longer written out for new files
- Use the MimeMap in preference to appending ",ttt" style hex suffixes when the type can be inferred from the extension
Tested on FreeBSD 13.0-RELEASE.