MOD: Added an exception being thrown when faultily requesting DefaultGUIContext
MOD: Added an exception being thrown when faultily requesting DefaultGUIContext

--HG--
branch : v0-8

cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two