Implement function to recursively add a dir to an iso tree.

This commit also to the following changes:
- create_node() on builder never frees the IsoFileSource, it is responsability 
  of the caller to free it.
- Recursive addition options added to IsoImage (not exposed to public API yet)
- create_node() takes care about follow_symlinks
- Added little demo program to test it.

Makefile.am

@@ -35,7 +35,8 @@ libinclude_HEADERS = \
 ## Build demo applications
 noinst_PROGRAMS = \
 	demo/lsl \
-	demo/cat 
+	demo/cat \
+	demo/tree 
 
 demo_lsl_CPPFLAGS = -Isrc
 demo_lsl_LDADD = $(src_libisofs_la_OBJECTS) $(THREAD_LIBS)
@@ -45,6 +46,10 @@ demo_cat_CPPFLAGS = -Isrc
 demo_cat_LDADD = $(src_libisofs_la_OBJECTS) $(THREAD_LIBS)
 demo_cat_SOURCES = demo/cat.c
 
+demo_tree_CPPFLAGS = -Isrc
+demo_tree_LDADD = $(src_libisofs_la_OBJECTS) $(THREAD_LIBS)
+demo_tree_SOURCES = demo/tree.c
+
 
 ## Build unit test