Init implementation of IsoFileSrc.

Ecma119Image, defined for first time in this commit, is the context for image 
written. It keeps the low level objects needed during image written.

IsoFileSrc is the low level object that takes care about the info needed to
write file contents to image. It takes care about reading from Stream in 2K
block chunks. To prevent the same file be written twice to image, we keep in
Ecma119Image a search tree, indexed by the triple key (fs, device, inode) that
uniquelly identifies a source.

src/ecma119.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2007 Vreixo Formoso
+ * 
+ * This file is part of the libisofs project; you can redistribute it and/or 
+ * modify it under the terms of the GNU General Public License version 2 as 
+ * published by the Free Software Foundation. See COPYING file for details.
+ */
+
+#ifndef LIBISO_ECMA119_H_
+#define LIBISO_ECMA119_H_
+
+typedef struct ecma119_image Ecma119Image;
+
+struct ecma119_image {
+    
+    unsigned int iso_level:2;
+
+    /* tree of files sources */
+    void *file_srcs;
+    int file_count;
+};
+
+#endif /*LIBISO_ECMA119_H_*/