Add a manual popover menu example

Reproduce the testpopover popover manually, by packing model
buttons into a stack in a popover.

tests/Makefile.am

@@ -9,7 +9,8 @@ AM_CPPFLAGS =				\
 	-I$(top_srcdir)/gdk		\
 	$(GTK_DEBUG_FLAGS)		\
 	$(GTK_DEP_CFLAGS)		\
-	$(GDK_DEP_CFLAGS)
+	$(GDK_DEP_CFLAGS)		\
+	-pthread
 
 DEPS = \
 	$(top_builddir)/gtk/libgtk-3.la
@@ -19,8 +20,12 @@ LDADD = \
 	$(top_builddir)/gdk/libgdk-3.la	\
 	$(GTK_DEP_LIBS)			\
 	$(GDK_DEP_LIBS)			\
+	-lgmodule-2.0			\
 	-lm
 
+AM_LDFLAGS = -Wl,--export-dynamic -pthread
+
+
 if USE_X11
 testsocket_programs = testsocket testsocket_child
 endif