I have #ifdef'd the calls you mentioned with GTK_CHECK_VERSION guards.

I also checked with one of the gnome/gtk devs and wrapping a
widget with strict ideas about its size is how you are supposed
to prevent its size from propagating: I suppose an alternative
would be some widget that doesn't resize or scroll at all,
but the basic approach would be the same.

I could not find a way to make overlay scrolbars behave, I think it's 
probably a bug in overlay scrollbars since classic scrollbars behave
just fine: I don't think that will be a problem as 3.16 is when overlay 
scrolling was introduced and that was also when the disabling function
was provided.