Fixed: a sheet's parent window did not become main

Sheets are like child windows, they can never become main. Previously, when an attempt was made to make a sheet the main window, its parent window did not become main as it should have. Thus the title bar would remain dimmed, even though the sheet was the key window.

With this commit, when a sheet is made main, it defers to the parent window.

AppKit/CPApplication.j

@@ -1025,7 +1025,7 @@ CPRunContinuesResponse  = -1002;
         var aWindow = [_windows objectAtIndex:count],
             context = aWindow._sheetContext;
 
-        if (context != nil && context["sheet"] === sheet)
+        if (context && context["sheet"] === sheet)
         {
             context["returnCode"] = returnCode;
             [aWindow _endSheet];

AppKit/CPWindow/CPWindow.j

@@ -871,7 +871,7 @@ CPTexturedBackgroundWindowMask
 {
 #if PLATFORM(DOM)
     // -dw- if a sheet is clicked, the parent window should come up too
-    if ([self isSheet])
+    if (_isSheet)
         [_parentView orderFront:self];
 
     if (!_isVisible)
@@ -2321,6 +2321,13 @@ CPTexturedBackgroundWindowMask
 */
 - (void)makeMainWindow
 {
+    // Sheets cannot be main. Their parent window becomes main.
+    if (_isSheet)
+    {
+        [_parentView makeMainWindow];
+        return;
+    }
+
     if ([CPApp mainWindow] === self || ![self canBecomeMainWindow])
         return;