Changelog entry for #1595 (plus add GIF)

src/common.h

@@ -140,6 +140,11 @@ namespace sharp {
   */
   ImageType DetermineImageType(char const *file);
 
+  /*
+    Does this image type support multiple pages?
+  */
+  bool ImageTypeSupportsPage(ImageType imageType);
+
   /*
     Open an image from the given InputDescriptor (filesystem, compressed buffer, raw pixel data)
   */