Move code for GUD tooltips from tooltip.el.

Move code for GUD tooltips from tooltip.el.
(require): CL needed to compile case.
(gud-tooltip-mode): Use to toggle GUD tooltips unstead of
tooltip-gud-tips-p. Make it a minor-mode.
(gud-find-file): Only prepare GUD tooltips if gud-tooltip-mode is t.
(gud-menu-map): GUD tooltips use gud-tooltip-mode now.
(gud-tooltip-modes, gud-tooltip-display, gud-tooltip-echo-area)
(gud-tooltip-change-major-mode)
(gud-tooltip-activate-mouse-motions-if-enabled)
(gud-tooltip-mouse-motions-active, gud-tooltip-activate-mouse-motions)
(gud-tooltip-mouse-motion, gud-tooltip-toggle-dereference)
(gud-tooltip-original-filter, gud-tooltip-dereference)
(gud-tooltip-event, tooltip-toggle-gud-tips)
(gud-tooltip-process-output, gud-tooltip-print-command)
(gud-tooltip-tips): Moved from tooltip.el.