replace fontrenderer.h include with forward declaration

in order to flatten the build dependency tree further, include
fontrenderer.h directly where needed, in header files a forward
declaration is enough

src/gui/lua/luainstance.cpp

@@ -34,6 +34,7 @@
 #include <gui/movieplayer.h>
 #include <driver/neutrinofonts.h>
 #include <driver/pictureviewer/pictureviewer.h>
+#include <driver/fontrenderer.h>
 #include <neutrino.h>
 #include <video_cs.h>
 

src/gui/lua/luainstance_helpers.h

@@ -46,6 +46,8 @@
 #define lua_unboxpointer(L, i) \
 	(*(void **)(lua_touserdata(L, i)))
 
+class Font;
+
 typedef std::pair<lua_Integer, Font*> fontmap_pair_t;
 typedef std::map<lua_Integer, Font*> fontmap_t;
 typedef fontmap_t::iterator fontmap_iterator_t;