SConstruct : Fix GafferImageUI linking on OSX
SConstruct : Fix GafferImageUI linking on OSX

boberfly/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,ivanimanishi/gaffer,boberfly/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,hradec/gaffer,boberfly/gaffer,hradec/gaffer,boberfly/gaffer,lucienfostier/gaffer,ivanimanishi/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,ivanimanishi/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,hradec/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,hradec/gaffer,ivanimanishi/gaffer,hradec/gaffer