Fix effect dialog layout glitches

QMdiSubWindow::setSizePolicy doesn't have any effect because QMdiSubWindow
uses a layout. This patch uses QMdiSubWindow::layout()->setSizeConstraint
instead. This may cause effects that don't have a layout and don't
implement sizeHint() to now be resizable. For effects that do though, it
fixes the size constraint.

src/gui/widgets/EffectView.cpp

@@ -29,6 +29,7 @@
#include <QMdiSubWindow>
#include <QPainter>
#include <QWhatsThis>
#include <QLayout>

#include "EffectView.h"
#include "DummyEffect.h"
@@ -109,7 +110,9 @@ EffectView::EffectView( Effect * _model, QWidget * _parent ) :
		{
			m_subWindow = gui->mainWindow()->addWindowedWidget( m_controlView );
			m_subWindow->setSizePolicy( QSizePolicy::Fixed, QSizePolicy::Fixed );
			m_subWindow->setFixedSize( m_subWindow->size() );
			if (m_subWindow->layout()) {
				m_subWindow->layout()->setSizeConstraint(QLayout::SetFixedSize);
			}

			Qt::WindowFlags flags = m_subWindow->windowFlags();
			flags &= ~Qt::WindowMaximizeButtonHint;