relax icon is not shown in "Global relax settings" window if running on a Mac.
This is as in revision 12856:
http://svn.gna.org/viewcvs/relax?rev=12856&view=rev),
but for the button "Settings" / "Global relax settings".
This change creates a bug, as the opened window upon clicking this button,
when closed, will have relax gui crash (with no button responding). This
needs to be fixed...
