#10662 use drawers for bibliography dialogs

This change solves dialog stacking problems on newer Mac OS X in combination with the OS provided file open dialog.

(cherry picked from commit 97dc585138)

src/frontends/qt4/GuiBibtex.cpp

@@ -57,6 +57,7 @@ GuiBibtex::GuiBibtex(GuiView & lv)
 	setupUi(this);
 
 	QDialog::setModal(true);
+	setWindowModality(Qt::WindowModal);
 
 	connect(okPB, SIGNAL(clicked()),
 		this, SLOT(slotOK()));

src/frontends/qt4/GuiBibtex.h

@@ -31,6 +31,7 @@ public:
 	{
 		Ui::BibtexAddUi::setupUi(this);
 		QDialog::setModal(true);
+		setWindowModality(Qt::WindowModal);
 	}
 };