Does .net core (dnx core 5.0) support filestream

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.NET

With the RC1 of .NET Core I went to investigate the most burning question in the back of my mind!
Can I open a damn FileStream to a file on the disk with .NET Core?
(And by that I mean anywhere, like "C:\temp\a.txt" and not just in $user\AppData !!!)

So I opened visual studio 2015, clicked new project > web > Console Application package (yes "web" is where the native app is!!)

then I typed "new FileStream" and looked at the helpful intellisense advice.

And it's where I got confused....

"new FileStream(....)" is:
- available for "DNX 4.5.1"
- NOT available for "DNX Core 5.0"

When I tried to compile

using (var s = new FileStream(@"c:\temp\a.txt", FileMode.Create))
using (var sw = new StreamWriter(s))
    sw.WriteLine("it worked!");

I got

Program.cs(13,32,13,42): DNX Core 5.0 error CS0246: The type or namespace name 'FileStream' could not be found (are you missing a using directive or an assembly reference?)
Program.cs(13,61,13,69): DNX Core 5.0 error CS0103: The name 'FileMode' does not exist in the current context

And YES I am using System.IO; it's an "issue" with ".NET Core"....

what does that means?!

What I have tried:

created a new .NET Core web app and looked at intellisense information