Fix some issues in window.el.

Fix some issues in window.el.

* window.el (window-make-atom): Don't overwrite parameter
already present.
(display-buffer-in-atom-window): Handle special case where we
split an already atomic window.
(window--major-non-side-window, display-buffer-in-side-window)
(window--side-check): Ignore minibuffer window when walking
window tree.
(window-deletable-p): Return 'frame only if no other frame uses
our minibuffer window.
(record-window-buffer): Run buffer-list-update-hook.
(split-window): Make sure window--check-frame won't destroy an
existing atomic window in case the new window gets nested
inside.
(display-buffer-at-bottom): Ignore minibuffer window when
walking window tree.  Don't split a side window.
(pop-to-buffer): Don't set-buffer here, the select-window call
should do that.
(mouse-autoselect-window-select): Autoselect only if we are in the
text portion of the window.