pgsql: Expand layer, namespace column widths

Presently the layer and namespace tables use type `varchar(128)` for
their respective name columns. For layer, this width works fine enough
using the sha256 digests provided by docker. However, if one wishes to
encode the image name into the layer  name (eg, to avoid collisions like
in [0]), the limit of 128 bytes starts to feel a bit cramped. Bump to
256 bytes, since that "ought to be enough for anybody." (TM)

[0]: https://github.com/coreos/clair/issues/319

database/pgsql/migrations/00007_expand_column_width.go

@@ -0,0 +1,31 @@
+// Copyright 2017 clair authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package migrations
+
+import "github.com/remind101/migrate"
+
+func init() {
+	RegisterMigration(migrate.Migration{
+		ID: 7,
+		Up: migrate.Queries([]string{
+			`ALTER TABLE Namespace ALTER COLUMN version_format SET DATA TYPE varchar(256);`,
+			`ALTER TABLE Layer ALTER COLUMN name SET DATA TYPE varchar(256);`,
+		}),
+		Down: migrate.Queries([]string{
+			`ALTER TABLE Namespace ALTER COLUMN version_format SET DATA TYPE varchar(128);`,
+			`ALTER TABLE Layer ALTER COLUMN name SET DATA TYPE varchar(128);`,
+		}),
+	})
+}