textmodes/ispell.el: Experimental support for support debugging.

textmodes/ispell.el: Experimental support for support debugging.

 * (ispell-create-debug-buffer): Create a `ispell-debug-buffer' debug
   buffer for ispell.
 * (ispell-print-if-debug): New function to print stuff to
   `ispell-debug-buffer' if debugging is enabled.
 * (ispell-region, ispell-process-line): Use `ispell-print-if-debug' to
   show some debugging info.
 * (ispell-buffer-with-debug): New function that creates a debugging
   buffer and calls `ispell-buffer' with debugging enabled.  This is also
   en example of a possible way to use this system.