Merge branch 'progsig-sx' into jgrpp

Conflicts:
	src/command.cpp
	src/command_type.h
	src/lang/english.txt
	src/rail_cmd.cpp
	src/rail_gui.cpp
	src/saveload/extended_ver_sl.cpp
	src/saveload/extended_ver_sl.h
	src/saveload/saveload.cpp
	src/widgets/rail_widget.h
	src/window_type.h

src/window_type.h

@@ -687,6 +687,11 @@ enum WindowClass {
 	 */
 	WC_TRACE_RESTRICT,
 
+	/**
+	 * Programmable signals window
+	 */
+	WC_SIGNAL_PROGRAM,
+
 	WC_INVALID = 0xFFFF, ///< Invalid window.
 };