Add GDK-PixBuf and librsvg2 as a dependency

They are required for JPEG exporting

src/ag-chart.c

@@ -10,6 +10,7 @@
 #include <locale.h>
 #include <math.h>
 #include <string.h>
+#include <librsvg/rsvg.h>
 
 #include "config.h"
 #include "astrognome.h"
@@ -41,6 +42,10 @@ typedef enum {
     XML_CONVERT_INT
 } XmlConvertType;
 
+#if !LIBRSVG_HAVE_CSS
+# error "We need RSVG CSS support to export charts as images!"
+#endif
+
 G_DEFINE_QUARK(ag_chart_error_quark, ag_chart_error);
 
 G_DEFINE_TYPE_WITH_PRIVATE(AgChart, ag_chart, GSWE_TYPE_MOMENT);