Add function to add an exiting file to the iso tree.

Node is created using a builder. Default builder and filesystem is added 
to IsoImage. Later we should expose setters for this atts.

src/libisofs.h

@@ -573,6 +573,35 @@ int iso_tree_add_new_symlink(IsoDir *parent, const char *name,
 int iso_tree_add_new_special(IsoDir *parent, const char *name, mode_t mode, 
                              dev_t dev, IsoSpecial **special);
 
+/**
+ * Add a new node to the image tree, from an existing file. 
+ * 
+ * TODO comment Builder and Filesystem related issues when exposing both
+ * 
+ * All attributes will be taken from the source file. The appropriate file
+ * type will be created.
+ * 
+ * @param image
+ *      The image
+ * @param parent
+ *      The directory in the image tree where the node will be added.
+ * @param path
+ *      The path of the file to add in the filesystem.
+ * @param node
+ *      place where to store a pointer to the newly added file. No 
+ *      extra ref is addded, so you will need to call iso_node_ref() if you 
+ *      really need it. You can pass NULL in this parameter if you don't need 
+ *      the pointer.
+ * @return
+ *     number of nodes in parent if success, < 0 otherwise
+ *     Possible errors:
+ *         ISO_NULL_POINTER, if image, parent or path are NULL
+ *         ISO_NODE_NAME_NOT_UNIQUE, a node with same name already exists
+ *         ISO_MEM_ERROR
+ */
+int iso_tree_add_node(IsoImage *image, IsoDir *parent, const char *path, 
+                      IsoNode **node);
+
 #define ISO_MSGS_MESSAGE_LEN 4096
 
 /**