golang#368 NewClient copies all settings from the context client

(cherry picked from commit 34851a6)

Author: Ferdy Pruis

Diff for: oauth2.go

@@ -343,11 +343,16 @@ func NewClient(ctx context.Context, src TokenSource) *http.Client {
 	if src == nil {
 		return internal.ContextClient(ctx)
 	}
+
+	cc := internal.ContextClient(ctx)
 	return &http.Client{
 		Transport: &Transport{
-			Base:   internal.ContextClient(ctx).Transport,
+			Base:   cc.Transport,
 			Source: ReuseTokenSource(nil, src),
 		},
+		CheckRedirect: cc.CheckRedirect,
+		Jar:           cc.Jar,
+		Timeout:       cc.Timeout,
 	}
 }