How to increase icon size of xfce4-panel window buttons (panel-tasklist-menu)

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http://askubuntu.com – After searching for a solution for a few days, I believe that this could be a bug. After increasing the height of the xfce-panel I noticed, that the icons of the window buttons remained small. Because this looks stupid and makes recognizing the icons harder than it has to be I want to increase the icon size of the window buttons of my xfce4-panel. I am running Linux Mint 14 Xfce, but this should affect everyone running Xfce 4.10. The xfce docs tell me that I "can set a custom icon size in gtk-icon-sizes with the name panel-tasklist-menu. The default icon size is 16px." (http://docs.xfce.org/x (HowTos)