Apply patch disabling the resume feature unless the resume file is specified by

the user (see FS#958). Kudos go to Andreas Lauser.

Note: I looked through the patch and asserted that the resume feature is still
working (I always overwrite the resume file anyway). In case dunecontrol stops
working for someone, please simply revert this patch (if possible) and add a
comment to FS#958).

[[Imported from SVN: r6520]]