Now that we have a one instance mode with DBus under linux, also make
it possible to use the "one-instance-when-started-from-file" and
"started-from-file" options.
Consider using --started-from-file in the file association scripts,
like what we do in the win32 NSIS script, so that all files opened
through the GUI are enqueued/played in the same instance.
(cherry picked from commit a8821cd8)