Move extensions.LabelSelector to unversioned.

Move type LabelSelector and type LabelSelectorRequirement from pkg/apis/extensions
This avoids an import loop when Job (and later DaemonSet, Deployment, ReplicaSet)
are moved out of extensions to new api groups.

Also Move LabelSelectorAsSelector utility from pkg/apis/extensions/ to pkg/api/unversioned/
Also its test.
Also LabelSelectorOp* constants.
Also the pkg/apis/extensions/validation functions ValidateLabelSelectorRequirement and
ValidateLabelSelector move to pkg/api/unversioned

The related type in pkg/apis/extensions/v1beta1/ is staying there.  I might move
it in another PR if neccessary.

pkg/api/unversioned/validation/validation.go

@@ -0,0 +1,53 @@
+/*
+Copyright 2015 The Kubernetes Authors All rights reserved.
+
+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 validation
+
+import (
+	"k8s.io/kubernetes/pkg/api/unversioned"
+	apivalidation "k8s.io/kubernetes/pkg/api/validation"
+	"k8s.io/kubernetes/pkg/util/validation/field"
+)
+
+func ValidateLabelSelector(ps *unversioned.LabelSelector, fldPath *field.Path) field.ErrorList {
+	allErrs := field.ErrorList{}
+	if ps == nil {
+		return allErrs
+	}
+	allErrs = append(allErrs, apivalidation.ValidateLabels(ps.MatchLabels, fldPath.Child("matchLabels"))...)
+	for i, expr := range ps.MatchExpressions {
+		allErrs = append(allErrs, ValidateLabelSelectorRequirement(expr, fldPath.Child("matchExpressions").Index(i))...)
+	}
+	return allErrs
+}
+
+func ValidateLabelSelectorRequirement(sr unversioned.LabelSelectorRequirement, fldPath *field.Path) field.ErrorList {
+	allErrs := field.ErrorList{}
+	switch sr.Operator {
+	case unversioned.LabelSelectorOpIn, unversioned.LabelSelectorOpNotIn:
+		if len(sr.Values) == 0 {
+			allErrs = append(allErrs, field.Required(fldPath.Child("values"), "must be specified when `operator` is 'In' or 'NotIn'"))
+		}
+	case unversioned.LabelSelectorOpExists, unversioned.LabelSelectorOpDoesNotExist:
+		if len(sr.Values) > 0 {
+			allErrs = append(allErrs, field.Forbidden(fldPath.Child("values"), "may not be specified when `operator` is 'Exists' or 'DoesNotExist'"))
+		}
+	default:
+		allErrs = append(allErrs, field.Invalid(fldPath.Child("operator"), sr.Operator, "not a valid selector operator"))
+	}
+	allErrs = append(allErrs, apivalidation.ValidateLabelName(sr.Key, fldPath.Child("key"))...)
+	return allErrs
+}