update proto library prior to avoid New* methods.
diffs generated automatically from Google-internal copy.
all tests pass
R=rsc, dsymonds1
CC=dsymonds
http://codereview.appspot.com/1908042
diff --git a/proto/encode.go b/proto/encode.go
index 9c323b2..fac4b5e 100644
--- a/proto/encode.go
+++ b/proto/encode.go
@@ -45,7 +45,9 @@
// ErrRequiredNotSet is the error returned if Marshal is called with
// a protocol buffer struct whose required fields have not
-// all been initialized.
+// all been initialized. It is also the error returned if Unmarshal is
+// called with an encoded protocol buffer that does not include all the
+// required fields.
var ErrRequiredNotSet = os.NewError("required fields not set")
// ErrRepeatedHasNil is the error returned if Marshal is called with