add MATE desktop support in xdg-settings
Submitted by Elan Ruusamäe
Assigned to Portland Bugs
MATE support was incomplete in b961235b it did not add support for xdg-settings which Google Chrome/Chromium uses to detect and set default browser.
MATE 1.5 uses same schema as gnome3, so shortcut to gnome3 methods
$ xdg-settings get default-web-browser chromium-browser.desktop
$ xdg-settings check default-web-browser chromium-browser.desktop yes