Improved code for keyboard and mouse grabbing and releasing to avoid

unnecessary actions. This relates loosely to bug 2955.

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>
(cherry picked from commit bc1b1fed7d)

src/kernel/qwidget_x11.cpp

@@ -1408,8 +1408,10 @@ void QWidget::grabMouse()
 void QWidget::grabMouse( const QCursor &cursor )
 {
     if ( !qt_nograb() ) {
-	if ( mouseGrb )
+	if ( mouseGrb != this ) {
+	    if ( mouseGrb ) {
 		mouseGrb->releaseMouse();
+	    }
 #if defined(QT_CHECK_STATE)
 	    int status =
 #endif
@@ -1431,6 +1433,7 @@ void QWidget::grabMouse( const QCursor &cursor )
 #endif
 	    mouseGrb = this;
 	}
+    }
 }
 
 /*!
@@ -1469,12 +1472,14 @@ void QWidget::releaseMouse()
 void QWidget::grabKeyboard()
 {
     if ( !qt_nograb() ) {
-	if ( keyboardGrb )
+	if ( keyboardGrb != this ) {
+	    if ( keyboardGrb ) {
 		keyboardGrb->releaseKeyboard();
-	XGrabKeyboard( x11Display(), winid, False, GrabModeAsync, GrabModeAsync,
-		       qt_x_time );
+	    }
+	    XGrabKeyboard( x11Display(), winid, False, GrabModeAsync, GrabModeAsync, qt_x_time );
 	    keyboardGrb = this;
 	}
+    }
 }
 
 /*!