Extract "pkg/version".PrintAndExitIfRequested() to its own package

because it causes a runtime panic if a binary which has its own implementation
of "-version" flag tries to reuse a package library which indirectly depend on
"pkg/version".

e.g. If such an user-defined binary tires to link "pkg/api" or "pkg/client",
the binary fails with a runtime panic "flag redefined: version".

pkg/version/flag/flag.go

@@ -0,0 +1,39 @@
+/*
+Copyright 2014 Google Inc. 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 flag defines utility functions to handle command line flags related to version of Kubernetes.
+package flag
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/version"
+)
+
+var (
+	versionFlag = flag.Bool("version", false, "Print version information and quit")
+)
+
+// PrintAndExitIfRequested will check if the -version flag was passed
+// and, if so, print the version and exit.
+func PrintAndExitIfRequested() {
+	if *versionFlag {
+		fmt.Printf("Kubernetes %s\n", version.Get())
+		os.Exit(0)
+	}
+}

pkg/version/version.go

@@ -17,13 +17,7 @@ limitations under the License.
 package version
 
 import (
-	"flag"
 	"fmt"
-	"os"
-)
-
-var (
-	versionFlag = flag.Bool("version", false, "Print version information and quit")
 )
 
 // Info contains versioning information.
@@ -49,12 +43,3 @@ func Get() Info {
 func (info Info) String() string {
 	return fmt.Sprintf("version %s.%s, build %s", info.Major, info.Minor, info.GitCommit)
 }
-
-// PrintAndExitIfRequested will check if the -version flag was passed
-// and, if so, print the version and exit.
-func PrintAndExitIfRequested() {
-	if *versionFlag {
-		fmt.Printf("Kubernetes %s\n", Get())
-		os.Exit(0)
-	}
-}