[Fix #915] Change position of guide-key popup window

[x-ji]

A fix for #915.

Previously situations like this would occur:

which makes it hard for new users to grasp what the commands are, if they vertically split windows.

Now at least they can all be displayed fully.

#1072 works fine for me. However if window-purpose is not to be incorporated soon, this could be a temporary fix?

[CestDiego]

This is very smat.... should be enough :)

[tuhdo]

I agree :)

[syl20bnr]

I wonder if we could use popwin with the same trick as helm.

[syl20bnr]

Thank you ! 👍
Will see what people say about this.
Cherry-picked into develop branch.

[mijoharas]

Hmm... I'm not sure about this, with the previous guide-key you could use ? or C-h to discover the full names of the commands. However, you are right that new users would not know to do this, so this is probably more discoverable.

That aside, I think there is a bug because when I trigger guide-key, my current buffers get moved to the side (to allocate space for the side buffer that is no-longer there, I assume) and I find this somewhat jarring.

Otherwise, it probably does make sense, I'm probably just still used to the old way of doing it and haven't trained myself to look down rather than to the side yet. 😄