(svn r1131) -Add: [Network] Autoclean_companies (set it with 'set autoclean_companies on/off').

When enabled, empty companies (companies with no active clients) with no 
 password are declared bankrupt after 1 year of emptyness.
For empty companies with password, the password is removed after 3 years 
 of emptyness.
The delay of removing company/password can be configured via:
 - 'set autoclean_protected <months>'
 - 'set autoclean_unprotected <months>'

misc.c

@@ -7,6 +7,8 @@
 #include "assert.h"
 #include "saveload.h"
 #include "network.h"
+#include "network_data.h"
+#include "network_server.h"
 
 extern void StartupEconomy();
 extern void InitNewsItemStructs();
@@ -667,6 +669,10 @@ void IncreaseDate()
 		TownsMonthlyLoop();
 		IndustryMonthlyLoop();
 		StationMonthlyLoop();
+#ifdef ENABLE_NETWORK
+		if (_network_server)
+			NetworkServerMonthlyLoop();
+#endif /* ENABLE_NETWORK */
 	}
 
 	/* check if we entered a new year? */