regexp: move to old/regexp, replace with exp/regexp

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5127042
diff --git a/src/pkg/index/suffixarray/suffixarray_test.go b/src/pkg/index/suffixarray/suffixarray_test.go
index aeac977..ec8796d 100644
--- a/src/pkg/index/suffixarray/suffixarray_test.go
+++ b/src/pkg/index/suffixarray/suffixarray_test.go
@@ -6,8 +6,8 @@
 
 import (
 	"bytes"
-	"exp/regexp"
 	"rand"
+	"regexp"
 	"sort"
 	"strings"
 	"testing"