Without this change, the spec parses <-c.(type) as (<-c).(type)
but parses <-c.(int) as <-(c.(int)).

With this change, the former parses as <-(c.(type)).

All three parsers already implement this rule, because
they look for the "type" word during parsing of a standard
type assertion.  This change merely brings the
spec in line with the implementations.

http://code.google.com/p/go/source/browse/src/cmd/gc/go.y#801
http://code.google.com/p/go/source/browse/src/pkg/go/parser/parser.go#900
http://gcc.gnu.org/viewcvs/branches/gccgo/gcc/go/parse.cc?revision=155389&view=markup#l2469

Pointed out by Brett Kail on golang-nuts.

R=gri
CC=golang-dev
https://golang.org/cl/182044