Renames a file on the local filesystem.
		
		This method can also be used to move a file to a whole other destination.
		
		See Also: WriteFile, CopyFile, DeleteFile
		
			Example - Example
			
				function OnStart()
				{
				    var oldfile = "test.txt";
				    var newfile = "test2.txt";
				    app.WriteFile( file, "Created: " + new Date() );
				    app.RenameFile( file, "/sdcard/wftest2.txt" );
				}