title: Error after migrating net core preview xproj to csproj
body: <p>I developed a net core class library using Net Core "1.0.0-preview2-003131" version. Currently using VS2015.
  But as this should be released soon, I want to move it to "1.0.1". 
  I installed this update: .NET Core 1.0.4 (<a href="https://github.com/dotnet/core/releases/tag/1.0.4" rel="nofollow noreferrer">https://github.com/dotnet/core/releases/tag/1.0.4</a>)</p>
  
  <p>When I change the version in my global.json I get this error:</p>
  
  <blockquote>
    <p>Severity  Code    Description Project File    Line    Suppression State
    Error   MSB4019 The imported project "C:\Program Files\dotnet\sdk\1.0.1\Microsoft\VisualStudio\v14.0\DotNet\Microsoft.DotNet.Props" was not found. Confirm that the path in the  declaration is correct, and that the file exists on disk.  </p>
  </blockquote>
  
  <p>So I read that doing "dotnet migrate" it changes my project from xproj to csproj, and the problem should be solved. </p>
  
  <p>But doing that, my csproj doesn't load properly, showing error:</p>
  
  <blockquote>
    <p>The default XML namespace of the project must be the MSBuild XML namespace. If the project is authored in the MSBuild 2003 format, please add xmlns="http://schemas.microsoft.com/developer/msbuild/2003" to the  element. If the project has been authored in the old 1.0 or 1.2 format, please convert it to MSBuild 2003 format.</p>
  </blockquote>