This is for consistency with other wrapping list constructors.
We want them all to be transfer full, allow-none.

Update all callers.

overlaylayout: Document minimally

See merge request GNOME/gtk!2285

This layout manager is not reusable, but we
still need to make its layout properties show
up in the docs.

Matthiasc/for master

See merge request GNOME/gtk!2284

Plug some holes in our structs by rearranging
a few fields. This is was done looking at
pahole output.

Plug some holes in our structs by rearranging
a few fields. This is was done looking at
pahole output.

The radius fields are never used.

We are using floats for rgb, and we don't need more precision
for hsl colors either. We use hsl for computing color expressions
like shade(), lighter() and darker(), which are not precisely
specified anyway.

This commit updates the one test where the output changes a
tiny bit due to this.