Add xclip.el.
* xclip.el: Better follow conventions.
Fix up copyright notice.
(xclip-program): Make it work in the usual way.
(xclip-set-selection, xclip-selection-value): Obey xclip-program.
(turn-on-xclip, turn-off-xclip): Don't autoload, not interactive.
(xclip-mode): New minor mode to avoid enabling it unconditionally.
* xclip.el: Some cleanups and fix copyright years.

(xclip-program, xclip-select-enable-clipboard): Use defcustom.
(xclip-select-text): Cleanup.
(turn-off-xclip): Remove.
(xclip-mode): Check xclip-program here.
* xclip.el: Use pbcopy and pbpaste if available

(xclip-use-pbcopy&paste): New variable.
(xclip-set-selection, xclip-selection-value, xclip-mode): Use it.
* xclip.el: Fix last change