(svn r5926) -Codechange: make _cur_year contain the full year, instead of the offset since 1920

-Codechange: store all year related variables that are _not_ stored in a savegame/transported over the network in the same format as _cur_year

bridge.h

@@ -12,7 +12,7 @@ enum {
 /** Struct containing information about a single bridge type
  */
 typedef struct Bridge {
-	byte avail_year;     ///< the year in which the bridge becomes available
+	Year avail_year;     ///< the year in which the bridge becomes available
 	byte min_length;     ///< the minimum length of the bridge (not counting start and end tile)
 	byte max_length;     ///< the maximum length of the bridge (not counting start and end tile)
 	uint16 price;        ///< the relative price of the bridge