Replace set_server_flag() with update_server_umode() and remove get_possible_umodes()

The idea here is not to expose the internal server implementation for storing umodes,
but instead have callers just work in terms of umode characters.

The 'possible umodes' have always been the same for all servers anyway.  We just assume
that [a-zA-Z] is the bounding set.

include/module.h

@@ -10,7 +10,7 @@
  * if we change the table below, we change this module number to the 
  * current date (YYYYMMDDxx where xx is a serial number).
  */
-#define MODULE_VERSION 2017112301UL
+#define MODULE_VERSION 2017120601UL
 
 #include "struct.h"
 
@@ -267,7 +267,7 @@ enum FUNCTION_VALUE
 	RESET_NICKNAME,
 /* various set server struct functions */
 	SET_SERVER_COOKIE,
-	SET_SERVER_FLAG,
+	UPDATE_SERVER_UMODE,
 	SET_SERVER_MOTD,
 	SET_SERVER_OPERATOR,
 	SET_SERVER_ITSNAME,
@@ -286,7 +286,6 @@ enum FUNCTION_VALUE
 	GET_SERVER_OPERATOR,
 	GET_SERVER_VERSION,
 	GET_SERVER_FLAG,
-	GET_POSSIBLE_UMODES,
 	GET_SERVER_PORT,
 	GET_SERVER_LAG,
 	GET_SERVER2_8,