Enable transferring of attribute using command 'repo manifest -o -'

'upstream' attribute is now transferred to the new manifest xml
that is created when using command 'repo manifest -o -'.

Manifest help is updated for the attributes 'sync-c','sync-s' and
'sync-j'.

Bug: Issue 164
Change-Id: If63f781e91d25c5b5b5ea0696b0c04337b0a686a
diff --git a/manifest_xml.py b/manifest_xml.py
index fdc3177..3517c15 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -261,6 +261,8 @@
         revision = self.remotes[remoteName].revision or d.revisionExpr
         if not revision or revision != p.revisionExpr:
           e.setAttribute('revision', p.revisionExpr)
+        if p.upstream and p.upstream != p.revisionExpr:
+          e.setAttribute('upstream', p.upstream)
 
       for c in p.copyfiles:
         ce = doc.createElement('copyfile')