Add dangling object and unreachable object in glossary.txt

[Yasushi SHOJI <yashi@atmark-techno.com>]

---
Would it be worth to add these two entery in
Documentation/glossary.txt?

English isn't my mother tang, so please check it.
-- 
         yashi



diff --git a/Documentation/glossary.txt b/Documentation/glossary.txt
index d20eb62..ee48009 100644
--- a/Documentation/glossary.txt
+++ b/Documentation/glossary.txt
@@ -73,6 +73,11 @@ DAG::
 	objects is acyclic (there is no chain which begins and ends with the
 	same object).
 
+dangling object::
+	An object which is a very special case of unreachable object;
+	it is not reachable from anything, including unreachable
+	objects.
+
 dircache::
 	You are *waaaaay* behind.
 
@@ -350,6 +355,9 @@ tag::
 unmerged index::
 	An index which contains unmerged index entries.
 
+unreachable object::
+	An object which is not reachable.
+
 working tree::
 	The set of files and directories currently being worked on,
 	i.e. you can work in your working tree without using git at all.