Implemented initial version of tree serialization which appears to work according to a simple test

( presort still needs implementation )
submodule: added stub to allow the tree to return something, its not implemented though

Author: Byron

lib/git/ext/gitdb

@@ -0,0 +1,15 @@
+import base
+
+
+class Submodule(base.IndexObject):
+	"""Implements access to a git submodule. They are special in that their sha
+	represents a commit in the submodule's repository which is to be checked out
+	at the path of this instance. 
+	The submodule type does not have a string type associated with it, as it exists
+	solely as a marker in the tree and index"""
+	
+	# this is a bogus type for base class compatability
+	type = 'submodule'
+	
+	# TODO: Add functions to retrieve a repo for the submodule, to allow 
+	# its initiailization and handling