title: VisualStudio 2015 is locking sln files on TFS after opening solution, however no changes to sln file
body: <p>Currently we use VS2015 and TFS 2015.</p>
  
  <p>Before using Visual Studio 2015 as a team, there were no problems.</p>
  
  <p>After starting to use VS2015, once you open a solution from source control explorer, visual studio is locking the solution file. 
  But it is not changing the file.</p>
  
  <p>This is so disturbing, because multiple warning messages shown right after opening a locked solution file.</p>
  
  <p>How can we solve this weird behaviour of VS2015?</p>