Don't use unsafe on appengine. Fixes #151.

safe.go

@@ -0,0 +1,7 @@
+// +build appengine
+
+package redis
+
+func bytesToString(b []byte) string {
+	return string(b)
+}

unsafe.go

@@ -1,3 +1,5 @@
+// +build !appengine
+
 package redis
 
 import (