Move test files to the 'pflag' package

This means we can avoid putting the repository name into the source
files, so people who have their own forks don't have to make changes.

bool_test.go

diff --git a/bool_test.go b/bool_test.go
index 19aa762..a2e1c5d 100644
--- a/bool_test.go
+++ b/bool_test.go
@@ -2,15 +2,13 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package pflag_test
+package pflag
 
 import (
 	"bytes"
 	"fmt"
 	"strconv"
 	"testing"
-
-	. "github.com/ogier/pflag"
 )
 
 // This value can be a boolean ("true", "false") or "maybe"

flag_test.go

diff --git a/flag_test.go b/flag_test.go
index aa8682f..82f7fae 100644
--- a/flag_test.go
+++ b/flag_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package pflag_test
+package pflag
 
 import (
 	"bytes"
@@ -12,8 +12,6 @@
 	"strings"
 	"testing"
 	"time"
-
-	. "github.com/ogier/pflag"
 )
 
 var (