Add support for loading trunk savegames versions 293 - 299 (12.0)

Use modified upstream saveload implementation for these versions
Re-arrange headers to support multiple saveload implementations

src/linkgraph/linkgraph.h

@@ -17,7 +17,7 @@
 #include "../station_base.h"
 #include "../cargotype.h"
 #include "../date_func.h"
-#include "../saveload/saveload.h"
+#include "../saveload/saveload_common.h"
 #include "linkgraph_type.h"
 #include <utility>
 
@@ -31,6 +31,13 @@ typedef Pool<LinkGraph, LinkGraphID, 32, 0xFFFF> LinkGraphPool;
 /** The actual pool with link graphs. */
 extern LinkGraphPool _link_graph_pool;
 
+namespace upstream_sl {
+	SaveLoadTable GetLinkGraphDesc();
+	SaveLoadTable GetLinkGraphJobDesc();
+	class SlLinkgraphNode;
+	class SlLinkgraphEdge;
+}
+
 /**
  * A connected component of a link graph. Contains a complete set of stations
  * connected by links as nodes and edges. Each component also holds a copy of
@@ -536,6 +543,11 @@ protected:
 	friend void Save_LinkGraph(LinkGraph &lg);
 	friend void Load_LinkGraph(LinkGraph &lg);
 
+	friend upstream_sl::SaveLoadTable upstream_sl::GetLinkGraphDesc();
+	friend upstream_sl::SaveLoadTable upstream_sl::GetLinkGraphJobDesc();
+	friend upstream_sl::SlLinkgraphNode;
+	friend upstream_sl::SlLinkgraphEdge;
+
 	CargoID cargo;         ///< Cargo of this component's link graph.
 	Date last_compression; ///< Last time the capacities and supplies were compressed.
 	NodeVector nodes;      ///< Nodes in the component.