Added test for checks of TIXIOpenDocument (external API).
Added test for checks of TIXIOpenDocument (external API).

melven/tixi,melven/tixi,DLR-SC/tixi,DLR-SC/tixi,melven/tixi,DLR-SC/tixi,melven/tixi,DLR-SC/tixi,DLR-SC/tixi,melven/tixi