Geom.ribbon in does not accept Int vectors as input when used with Geom.smooth

[espintos]

Geom.ribbon does't accept Int vectors as input for ymin and ymax when used in combination with Geom.smooth.

http://stackoverflow.com/questions/28966555/geom-ribbon-in-gadfly-julia-does-not-accept-int-vectors-as-input

[IainNZ]

At a glance, looks like can relax the T to T,S and use a promote_type to keep it type stable

[dcjones]

I don't get this error on julia 0.3 or 0.4 on gadfly master. Maybe it's accidentally fixed already?

[Mattriks]

I can't reproduce this either on Julia 0.5 and Gadfly 0.6, so this issue should be closed?

x = [-10:10;]
y = x.^2
ymin = y-10
ymax = y+10

p = plot(x=x, y=y,  ymin=ymin, ymax=ymax, Geom.smooth, Geom.ribbon)