go/types: moved from exp/types

This is a just a file move with no other changes
besides the manual import path adjustments in these
two files:

src/pkg/exp/gotype/gotype.go
src/pkg/exp/gotype/gotype_test.go

Note: The go/types API continues to be subject to
possibly significant changes until Go 1.1. Do not
rely on it being stable at this point.

R=adonovan
CC=golang-dev
https://golang.org/cl/7013049

src/pkg/exp/gotype/gotype.go

@@ -6,13 +6,13 @@ package main
 
 import (
 	"errors"
-	"exp/types"
 	"flag"
 	"fmt"
 	"go/ast"
 	"go/parser"
 	"go/scanner"
 	"go/token"
+	"go/types"
 	"io/ioutil"
 	"os"
 	"path/filepath"

src/pkg/exp/gotype/gotype_test.go

@@ -117,7 +117,6 @@ var tests = []string{
 	"flag",
 	"fmt",
 
-	"exp/types",
 	"exp/gotype",
 
 	"go/ast",
@@ -128,6 +127,7 @@ var tests = []string{
 	"go/printer",
 	"go/scanner",
 	// "go/token",
+	"go/types",
 
 	"hash/adler32",
 	"hash/crc32",