chamelium: Add support for VGA frame comparison testing

This adds support for VGA frame comparison testing with the reference
generated from cairo. The retrieved frame from the chamelium is first
cropped, as it contains the blanking intervals, through a dedicated
helper. Another helper function asserts that the analog frame
matches or dump it to png if not.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@linux.intel.com>
Reviewed-by: Lyude <lyude@redhat.com>
diff --git a/configure.ac b/configure.ac
index 7ea768e..dec3e92 100644
--- a/configure.ac
+++ b/configure.ac
@@ -197,6 +197,10 @@
 	if test x"$glib" != xyes; then
 		AC_MSG_ERROR([Failed to find glib, required by chamelium. Use --disable-chamelium to disable chamelium support.])
 	fi
+	if test x"$gsl" != xyes; then
+		AC_MSG_ERROR([Failed to find gsl, required by chamelium. Use --disable-chamelium to disable chamelium support.])
+	fi
+
 	AC_DEFINE(HAVE_CHAMELIUM, 1, [Enable Chamelium support])
 fi