Fixed bug#19576: `write-file' saves wrong buffer.

Fixed bug#19576: `write-file' saves wrong buffer.

If a function on the hook `window-size-change-functions' doesn't
restore the current buffer, functions that save and restore the
current window configuration (like `y-or-no-p') could silently
change the current buffer.  When `write-file' asked the user
confirmation to overwrite a file, `y-or-no-p' changed the current
buffer, and the wrong buffer was saved to the file.

* lisp/follow.el (follow-windows-start-end): Call `select-frame'
using the `norecord' parameter.
(follow-window-size-change): Restore current buffer. Call
`select-frame' using the `norecord' parameter. Cleanup.