New API call iso_file_source_get_aa_string()

and IsoFileSource_Iface.version == 1 with ifs_class
Now libisofs is able to load AA strings from images and to store them again.

libisofs/fsource.c

@@ -115,3 +115,17 @@ IsoFilesystem* iso_file_source_get_filesystem(IsoFileSource *src)
 {
     return src->class->get_filesystem(src);
 }
+
+
+/* ts A90115 */
+inline
+int iso_file_source_get_aa_string(IsoFileSource *src,
+                                  unsigned char **aa_string, int flag)
+{
+    if (src->class->version < 1) {
+        *aa_string = NULL;
+        return 1;
+    }
+    return src->class->get_aa_string(src, aa_string, flag);
+}
+