Added so that we can check if the system library has been loaded by querying: SFML::SystemLoaded which will be true if loaded otherwise nil which counts as false in an if-statement

git-svn-id: https://sfml.svn.sourceforge.net/svnroot/sfml/branches/sfml2@1596 4e206d99-4929-0410-ac5d-dfc041789085

ruby/sfml-system/system/System.cpp

@@ -35,6 +35,7 @@ VALUE GetNamespace( void )
 void Init_system( void )
 {
 	globalSFMLNamespace = rb_define_module( "SFML" );
+	rb_define_const(globalSFMLNamespace, "SystemLoaded", Qtrue);
 	Init_Clock();
 	Init_Vector2();
 	Init_Vector3();