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.

src/linkgraph/linkgraphjob.h

@@ -27,6 +27,10 @@ typedef Pool<LinkGraphJob, LinkGraphJobID, 32, 0xFFFF> LinkGraphJobPool;
 /** The actual pool with link graph jobs. */
 extern LinkGraphJobPool _link_graph_job_pool;
 
+namespace upstream_sl {
+	SaveLoadTable GetLinkGraphJobDesc();
+}
+
 /**
  * Class for calculation jobs to be run on link graphs.
  */
@@ -57,6 +61,7 @@ private:
 	typedef SmallMatrix<EdgeAnnotation> EdgeAnnotationMatrix;
 
 	friend SaveLoadTable GetLinkGraphJobDesc();
+	friend upstream_sl::SaveLoadTable upstream_sl::GetLinkGraphJobDesc();
 	friend void GetLinkGraphJobDayLengthScaleAfterLoad(LinkGraphJob *lgj);
 	friend class LinkGraphSchedule;
 	friend class LinkGraphJobGroup;

src/linkgraph/linkgraphschedule.h

@@ -16,6 +16,10 @@
 
 class LinkGraphJob;
 
+namespace upstream_sl {
+	SaveLoadTable GetLinkGraphScheduleDesc();
+}
+
 /**
  * A handler doing "something" on a link graph component. It must not keep any
  * state as it is called concurrently from different threads.
@@ -42,6 +46,7 @@ private:
 	typedef std::list<LinkGraph *> GraphList;
 	typedef std::list<std::unique_ptr<LinkGraphJob>> JobList;
 	friend SaveLoadTable GetLinkGraphScheduleDesc();
+	friend upstream_sl::SaveLoadTable upstream_sl::GetLinkGraphScheduleDesc();
 
 protected:
 	std::unique_ptr<ComponentHandler> handlers[6]; ///< Handlers to be run for each job.