Added feature to print a <notice> from manifest at the end of a sync.

This feature is used to convey information on a when a branch has
ceased development or if it is an experimental branch with a few
gotchas, etc.

You add it to your manifest XML by doing something like this:
<manifest>
  <notice>
    NOTE TO DEVELOPERS:
      If you checkin code, you have to pinky-swear that it contains no bugs.
      Anyone who breaks their promise will have tomatoes thrown at them in the
      team meeting.  Be sure to bring an extra set of clothes.
  </notice>

  <remote ... />
  ...
</manifest>

Carriage returns and indentation are relevant for the text in this tag.

This feature was requested by Anush Elangovan on the ChromiumOS team.

docs/manifest-format.txt

@@ -20,12 +20,15 @@ A manifest XML file (e.g. 'default.xml') roughly conforms to the
 following DTD:
 
   <!DOCTYPE manifest [
-    <!ELEMENT manifest (remote*,
+    <!ELEMENT manifest (notice?,
+                        remote*,
                         default?,
                         manifest-server?,
                         remove-project*,
                         project*)>
   
+    <!ELEMENT notice (#PCDATA)>
+  
     <!ELEMENT remote (EMPTY)>
     <!ATTLIST remote name         ID    #REQUIRED>
     <!ATTLIST remote fetch        CDATA #REQUIRED>