note on extensions

git-svn-id: https://protobuf-c.googlecode.com/svn/trunk@90 00440858-1255-0410-a3e6-75ea37f81c3a

TODO

@@ -8,6 +8,10 @@
     whose name is built from the package, the base message type-name
     and the member.  which takes the base message and returns the
     value, if it is found in "unknown_values".
+    boolean package__extension_member_name__get(Message *message,
+                                                type     *out);
+    void    package__extension_member_name__set_raw(type      in,
+                                                ProtobufCUnknownValue *to_init);
 - ensure enums are int-size
 
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