Left and right wall length overestimated

[cefn]

At the left and right, the wall length is slightly more than necessary, creating a slight lip. I saw this as a feature to help keep pens in, but Clare and others may see it as a flaw, so let's fix it for rc3.

It may be possible to reverse the overlap, although this would mean that the exposed ply edge is visible on the sides instead of the bottom. Probably not an issue, but should be thought about.

The benefit of reversing the overlap is to be able to add the 1-2mm consistently along the right wall, instead of just where the middle section is glued.

[clarebowman22]

If we decided that an overlap was a useful feature then the overlap should be more obvious (extend its length a further 4/5mm). However I still am sticking to the idea that we don't need an overlap and it looks like a design mistake.