reftests: Add label-sizing test

Checks that the size requests for labels are as they should be for
required and natural size given various combinations of wrap, ellipsize,
width-chars and max-width-chars.

See
http://mail.gnome.org/archives/gtk-devel-list/2011-April/msg00036.html
for the discussion spawning this test.

tests/reftests/Makefile.am

@@ -25,5 +25,8 @@ clean-local:
 	rm -rf output/ || true
 
 EXTRA_DIST += \
+	label-sizing.css \
+	label-sizing.ref.ui \
+	label-sizing.ui \
 	simpe.ref.png \
 	simple.ui

tests/reftests/label-sizing.css

@@ -0,0 +1,7 @@
+* {
+  font: Monospace 12
+}
+
+GtkPaned GtkEventBox {
+  background-color: pink
+}