Fixed: CPPanel could not always become the key window.

Without this fix, `CPPanel` followed the same rules as `CPWindow` with regards to becoming the key window. But `CPPanel` is supposed to always be willing to become the key window, as stated in its documentation.

This change makes `CPPanel` always return `YES` for `canBecomeKeyWindow`.

AppKit/CPPanel.j

@@ -114,4 +114,9 @@ CPDocModalWindowMask    = 1 << 6;
     return NO;
 }
 
+- (BOOL)canBecomeKeyWindow
+{
+  return YES;
+}
+
 @end