Add vi-style "jump" commands for copy mode, from Micah Cowan.

tmux.h

@@ -459,6 +459,10 @@ enum mode_key_cmd {
 	MODEKEYCOPY_HALFPAGEUP,
 	MODEKEYCOPY_HISTORYBOTTOM,
 	MODEKEYCOPY_HISTORYTOP,
+	MODEKEYCOPY_JUMP,
+	MODEKEYCOPY_JUMPAGAIN,
+	MODEKEYCOPY_JUMPREVERSE,
+	MODEKEYCOPY_JUMPBACK,
 	MODEKEYCOPY_LEFT,
 	MODEKEYCOPY_MIDDLELINE,
 	MODEKEYCOPY_NEXTPAGE,