-allow any window to become a sheet

AppKit/CPWindow/_CPDocModalWindowView.j

@@ -54,4 +54,9 @@ var _CPStandardWindowViewBodyBackgroundColor = nil;
     return aContentRect;
 }
 
+- (void)_enableSheet:(BOOL)enable
+{
+	// do nothing, already a sheet
+}
+
 @end