Add El-Torito estructures to an IsoImage, and APIs for manage it.

src/fsource.h

@@ -19,6 +19,10 @@
 
 #include <sys/stat.h>
 
+#define ISO_LOCAL_FS_ID        1
+#define ISO_IMAGE_FS_ID        2
+#define ISO_ELTORITO_FS_ID     3
+
 typedef struct Iso_File_Source IsoFileSource;
 typedef struct Iso_Filesystem IsoFilesystem;