goprotobuf: update due to name change of reflect.ArrayCopy (now reflect.Copy)

R=nigeltao, dsymonds
CC=golang-dev
http://codereview.appspot.com/3666041

proto/text_parser.go

@@ -371,7 +371,7 @@ func (p *textParser) readAny(v reflect.Value, props *Properties) *ParseError {
 		flen := fv.Len()
 		if flen == fv.Cap() {
 			nav := reflect.MakeSlice(at, flen, 2*flen+1)
-			reflect.ArrayCopy(nav, fv)
+			reflect.Copy(nav, fv)
 			fv.Set(nav)
 		}
 		fv.SetLen(flen + 1)