Handle complex arguments in imagesc (bug #36866) * image.m: Don't error out with complex images, show real part and warn, like imshow. * graphics.in.h (array_property): Change type_constraint to std::set instead of std::list. (array_property::add_constraint): Use std::set::insert instead of std::list::push_back. (image::properties::init): Add new "real" constraint. * graphics.cc (array_property::validate): Check for new "real" type constraint. * gl-render.cc (opengl_renderer::draw_image): Abort if no image data is found.