Cocoa: remove current contentView when clearing window

Otherwise they might be still events sent to view with no
proper QWindow. Also, add dealloc QNSView for clean up.

Task-number: QTBUG-26580
Task-number: QTBUG-27456
Change-Id: Icdbe5c39490b72ec82795c2d71e5671cea81921e
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -713,6 +713,7 @@ void QCocoaWindow::setNSWindow(NSWindow *window)
 
 void QCocoaWindow::clearNSWindow(NSWindow *window)
 {
+    [window setContentView:nil];
     [window setDelegate:nil];
     [window clearPlatformWindow];
     [[NSNotificationCenter defaultCenter] removeObserver:m_contentView];

src/plugins/platforms/cocoa/qnsview.mm

@@ -89,6 +89,14 @@ static QTouchDevice *touchDevice = 0;
     return self;
 }
 
+- (void)dealloc
+{
+    CGImageRelease(m_cgImage);
+    m_cgImage = 0;
+    m_window = 0;
+    [super dealloc];
+}
+
 - (id)initWithQWindow:(QWindow *)window platformWindow:(QCocoaWindow *) platformWindow
 {
     self = [self init];