input: distinguish <Alt+Left> from <Alt+Right> on an rxvt terminal

Both would jump a word to the left -- now each jumps a word in the
proper direction.

src/winio.c

@@ -401,10 +401,10 @@ int parse_kbinput(WINDOW *win)
 			retval = KEY_END;
 			break;
 		    case 'C':
-			retval = controlright;
+			retval = CONTROL_RIGHT;
 			break;
 		    case 'D':
-			retval = controlleft;
+			retval = CONTROL_LEFT;
 			break;
 		    case 'a':
 			retval = shiftaltup;