I made a new thread, as the final diff is ready that adds the
functionality of https://www.emacswiki.org/emacs/TransposeFrame, and a
lot more (rotating subtrees, 'cycling' windows such as in
https://github.com/daichirata/emacs-rotate).

This diff that adds the required modifications to window.c and window.el
and window.texi done by Martin as well, and adds window-x.el which
contains all the elisp functions which add the interactive functions.

This diff updates NEWS as well, and doesn't add any keybindings for the
functions.