speed up un-cached directories

embedded thumbnails will be used for the first pass when cached thumbnails are not found.

rtengine/imageio.h

@@ -72,6 +72,8 @@ class ImageIO {
         int loadJPEG (Glib::ustring fname);
         int loadTIFF (Glib::ustring fname);
 
+        int loadJPEGFromMemory (const char* buffer, int bufsize);
+
         int savePNG  (Glib::ustring fname, int compression = -1, int bps = -1);
         int saveJPEG (Glib::ustring fname, int quality = 100);
         int saveTIFF (Glib::ustring fname, int bps = -1, bool uncompressed = false);