2023-08-10  Richard Hopkins  <xemacs@unbit.co.uk>

	* em-unix.el (eshell/diff): Wrap #'diff with #'window-buffer as
	`with-current-buffer' requires a buffer and #'diff returns a
	window showing the diff contents.  Previously...

	M-x eshell
	echo a > a.txt
	echo b > b.txt
	diff -u a.txt b.txt
	=> Wrong type argument: stringp, #<window on "*Diff Output*" 0x7>

	#'diff now executes without error and pops up a buffer in
	#'diff-mode with the output.