[LyX/master] Reintroduce some class definitions.

[Stephan Witt]

commit 5af8238700785c4d4769809d5b91bd8a6e7e8780
Author: Stephan Witt <sw...@lyx.org>
Date:   Sun Aug 24 21:40:40 2014 +0200

    Reintroduce some class definitions.

diff --git a/src/frontends/qt4/GuiApplication.h 
b/src/frontends/qt4/GuiApplication.h
index 79da314..5e4cda2 100644
--- a/src/frontends/qt4/GuiApplication.h
+++ b/src/frontends/qt4/GuiApplication.h
@@ -19,6 +19,8 @@
 #include <QList>
 
 class QAbstractItemModel;
+class QIcon;
+class QSessionManager;
 
 namespace lyx {