Add a way to override the revision of an 

This change adds support for the 'revision' attribute in
. This avoids the need to perform a 
followed by a  in local manifests.

Change-Id: Id2834fcfc1ae0d74b3347bed3618f250bf696b1f
diff --git a/docs/manifest-format.txt b/docs/manifest-format.txt
index 0e6cbe3..56bdf14 100644
--- a/docs/manifest-format.txt
+++ b/docs/manifest-format.txt
@@ -86,6 +86,7 @@
     
     
     
+    
 
     
     
@@ -300,6 +301,9 @@
 Attribute `groups`: List of additional groups to which this project
 belongs.  Same syntax as the corresponding element of `project`.
 
+Attribute `revision`: If specified, overrides the revision of the original
+project.  Same syntax as the corresponding element of `project`.
+
 Element annotation
 ------------------