MouseEvent buttonDown should be based on the left mouse button only (close #520)
MouseEvent buttonDown should be based on the left mouse button only (close #520)

openfl/openfl,NenadBojkovski/openfl,Gama11/openfl,NenadBojkovski/openfl,openfl/openfl,Gama11/openfl,Gama11/openfl,openfl/openfl,Gama11/openfl