Add a 'post-commit' hook.

For now do nothing but chain to a project-specific hook.

post-commit

+#!/usr/bin/env bash
+#=============================================================================
+# Copyright 2010-2015 Kitware, Inc.
+#
+# 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.
+#=============================================================================
+
+. "${BASH_SOURCE%/*}/hooks-config.bash"
+
+# Chain to project-specific hook.
+hooks_chain post-commit "$@"