Library list sources

calling library.get_sources() will iterate over the list of sources
contained in the library.  This is mostly used for storing in the backup
xml.

libsaria/sources/library.py

@@ -93,6 +93,10 @@ def walk():
 	for tag in tag_tree.walk():
 		yield tag[3]
 
+def get_sources():
+	for source in sources:
+		yield source
+
 def file_to_id(file):
 	return os.stat(file).st_ino