(svn r6108) -NewGRF Feature: Implement currencies replacment via grf file.

All properties can now be modified i.e:
Introduction date for euro conversion
Currency name, decimal separator, currency symbol (before or after amount)
and the rate compared to the base currency, the british pound

currency.h

@@ -6,6 +6,8 @@
 enum {
 	CF_NOEURO = 0,
 	CF_ISEURO = 1,
+	NUM_CURRENCY = 25,
+	CUSTOM_CURRENCY_ID = NUM_CURRENCY + 1,
 };
 
 typedef struct {
@@ -14,17 +16,24 @@ typedef struct {
 	Year to_euro;
 	char prefix[16];
 	char suffix[16];
+	/**
+	 * Position of the currency symbol on the amount string.
+	 * 0 = placed before, 1 = placed after
+	 */
+	byte symbol_pos;
+	StringID name;
 } CurrencySpec;
 
-extern CurrencySpec _currency_specs[];
-extern const StringID _currency_string_list[];
+
+extern CurrencySpec _currency_specs[NUM_CURRENCY];
 
 // XXX small hack, but makes the rest of the code a bit nicer to read
-#define CUSTOM_CURRENCY_ID 24
 #define _custom_currency (_currency_specs[CUSTOM_CURRENCY_ID])
 #define _currency ((const CurrencySpec*)&_currency_specs[_opt_ptr->currency])
 
 uint GetMaskOfAllowedCurrencies(void);
 void CheckSwitchToEuro(void);
+void ResetCurrencies(void);
+StringID* BuildCurrencyDropdown(void);
 
 #endif /* CURRENCY_H */