title: Checkout branch in Git Extensions creates branch with uppercase name
body: <p>When I check out a branch by right-clicking on the branch and choosing "Checkout Branch | origin/f/xxxx",  I see the following dialog box.  After pressing checkout,  it seems that the local branch is named with an uppercase letter.  (See highlight)  When I push to the remote (on GitHub),  I am asked to create a new tracking reference on the server and a new branch is created because it is case sensitive.   The UI doesn't allow me to push to "f/xxxx" or rename the branch.</p>
  
  <p>I've checked my ignore case setting:</p>
  
  <blockquote>
    <p>$ git config --get core.ignorecase </p>
    
    <p>true</p>
  </blockquote>
  
  <p>Any idea why this happens?</p>
  
  <p>Thanks</p>