EffectView: fixed artifacts with semitransparent widget shadow

We must not set the Qt::WA_OpaquePaintEvent attribute when using a
semitransparent background image in paintEvent(). Fixes artifacts
in EffectView's shadowed border.
(cherry picked from commit d830e7f622)

src/gui/widgets/EffectView.cpp

@@ -1,5 +1,5 @@
 /*
- * effect_view.cpp - view-component for an effect
+ * EffectView.cpp - view-component for an effect
  *
  * Copyright (c) 2006-2007 Danny McRae <khjklujn/at/users.sourceforge.net>
  * Copyright (c) 2007-2010 Tobias Doerffel <tobydox/at/users.sourceforge.net>
@@ -51,8 +51,6 @@ EffectView::EffectView( Effect * _model, QWidget * _parent ) :
 {
 	setFixedSize( 210, 60 );
 
-	setAttribute( Qt::WA_OpaquePaintEvent, true );
-
 	m_bypass = new ledCheckBox( "", this );
 	m_bypass->move( 3, 3 );
 	m_bypass->setWhatsThis( tr( "Toggles the effect on or off." ) );