refactor undo_action class

First we split the undo_ation into subclasses (undo_action_base, undo_action
and shroud_clearing_action) so that undo actions that don't clear shroud don't
contain the route and view_info data.
Also the non undoable actions now don't need to implement undo() and redo()

Second we move the undo action classes to different files.

src/CMakeLists.txt

@@ -701,7 +701,14 @@ set(wesnoth-main_SRC
 	actions/create.cpp
 	actions/heal.cpp
 	actions/move.cpp
+	actions/shroud_clearing_action.cpp
 	actions/undo.cpp
+	actions/undo_action.cpp
+	actions/undo_dismiss_action.cpp
+	actions/undo_move_action.cpp
+	actions/undo_recall_action.cpp
+	actions/undo_recruit_action.cpp
+	actions/undo_update_shroud_action.cpp
 	actions/vision.cpp
 	addon/client.cpp
 	addon/info.cpp

src/SConscript

@@ -189,7 +189,14 @@ wesnoth_sources = Split("""
     actions/create.cpp
     actions/heal.cpp
     actions/move.cpp
+    actions/shroud_clearing_action.cpp
     actions/undo.cpp
+    actions/undo_action.cpp
+    actions/undo_dismiss_action.cpp
+    actions/undo_move_action.cpp
+    actions/undo_recall_action.cpp
+    actions/undo_recruit_action.cpp
+    actions/undo_update_shroud_action.cpp
     actions/vision.cpp
     addon/client.cpp
     addon/info.cpp

src/actions/shroud_clearing_action.cpp

@@ -0,0 +1 @@
+#include "shroud_clearing_action.hpp"

src/actions/shroud_clearing_action.hpp

@@ -0,0 +1,53 @@
+#pragma once
+
+#include "vision.hpp"
+#include "../map_location.hpp"
+#include "../unit_ptr.hpp"
+
+#include <boost/noncopyable.hpp>
+#include <boost/ptr_container/ptr_vector.hpp>
+#include <boost/optional.hpp>
+namespace actions
+{
+/// base class for classes that clear srhoud (move/recruit/recall)
+struct shroud_clearing_action
+{
+
+	shroud_clearing_action(const config& cfg)
+		: route()
+		, view_info(cfg.child_or_empty("unit"))
+	{
+		read_locations(cfg, route);
+	}
+
+	shroud_clearing_action(const unit_const_ptr u, const map_location& loc)
+		: route(1, loc)
+		, view_info(*u)
+	{
+
+	}
+
+	typedef std::vector<map_location> t_route;
+
+	shroud_clearing_action(const unit_const_ptr u, const t_route::const_iterator& begin, const t_route::const_iterator& end)
+		: route(begin, end)
+		, view_info(*u)
+	{
+
+	}
+
+	/// The hexes occupied by the affected unit during this action.
+	/// For recruits and recalls this only contains one hex.
+	t_route route;
+	/// A record of the affected unit's ability to see.
+	clearer_info view_info;
+
+	void write(config & cfg) const
+	{
+		write_locations(route, cfg);
+		view_info.write(cfg.add_child("unit"));
+	}
+
+	virtual ~shroud_clearing_action() {}
+};
+}