(svn r5070) Merged the bridge branch

-Feature: Bridges can now be placed above:
	Any railway track combination (excluding depots and waypoints)
	Any road combination (excluding depots)
	Clear tiles (duh), including fields
	Tunnel entrances
	Bridge heads

Thanks to Tron for idea and implementation, KUDr for the yapf synchronization and many others for hours of testing

There are still a number of visual problems remaining, especially when electric railways are on or under the bridge.
DO NOT REPORT THOSE BUGS FOR THE TIME BEING please.

bridge_map.c

@@ -3,22 +3,25 @@
 #include "stdafx.h"
 #include "openttd.h"
 #include "bridge_map.h"
+#include "variables.h"
 
 
 TileIndex GetBridgeEnd(TileIndex tile, DiagDirection dir)
 {
 	TileIndexDiff delta = TileOffsByDir(dir);
 
-	assert(DiagDirToAxis(dir) == GetBridgeAxis(tile));
-
-	do {
-		tile += delta;
-	} while (!IsBridgeRamp(tile));
+	do { tile += delta; } while (IsBridgeAbove(tile) && IsBridgeOfAxis(tile, DiagDirToAxis(dir)));
 
 	return tile;
 }
 
 
+TileIndex GetNorthernBridgeEnd(TileIndex t)
+{
+	return GetBridgeEnd(t, ReverseDiagDir(AxisToDiagDir(GetBridgeAxis(t))));
+}
+
+
 TileIndex GetSouthernBridgeEnd(TileIndex t)
 {
 	return GetBridgeEnd(t, AxisToDiagDir(GetBridgeAxis(t)));
@@ -27,11 +30,25 @@ TileIndex GetSouthernBridgeEnd(TileIndex t)
 
 TileIndex GetOtherBridgeEnd(TileIndex tile)
 {
-	TileIndexDiff delta = TileOffsByDir(GetBridgeRampDirection(tile));
-
-	do {
-		tile += delta;
-	} while (!IsBridgeRamp(tile));
-
-	return tile;
+	assert(IsBridgeTile(tile));
+	return GetBridgeEnd(tile, GetBridgeRampDirection(tile));
+}
+
+uint GetBridgeHeight(TileIndex tile, Axis a)
+{
+	uint h, f;
+	uint tileh = GetTileSlope(tile, &h);
+
+	f = GetBridgeFoundation(tileh, a);
+
+	if (f) {
+		if (f < 15) {
+			h += TILE_HEIGHT;
+			tileh = SLOPE_FLAT;
+		} else {
+			tileh = _inclined_tileh[f - 15];
+		}
+	}
+
+	return h + TILE_HEIGHT;
 }