Merge pull request #161 from cockroachdb/davidh/add-errunsupported

errors: re-export ErrUnsupported from stdlib

Author: dhartunian

errutil_api.go

@@ -15,11 +15,19 @@
 package errors
 
 import (
+	"errors"
+
 	"github.com/cockroachdb/errors/barriers"
 	"github.com/cockroachdb/errors/errbase"
 	"github.com/cockroachdb/errors/errutil"
 )
 
+// ErrUnsupported indicates that a requested operation cannot be
+// performed, because it is unsupported. This is the same value as
+// the standard library's errors.ErrUnsupported, re-exported here
+// for drop-in compatibility.
+var ErrUnsupported = errors.ErrUnsupported
+
 // New creates an error with a simple error message.
 // A stack trace is retained.
 //