title: GIT: move back to an old commit and merge that with master
body: <p>Given a project with 2 files: <code>fileA</code> and <code>fileB</code>. Both were once added to a git-repository. Then I added <code>fileA</code> to <code>.gitignore</code> (and flushed the git-cache), so that in the current master only <code>fileB</code> is present. I would like to clone this repository to another machine now, but fileA is missing.</p>
  
  <p>The next thing I did was to create a branch from the commit where both files were present. The big question now is: how do I get back to the master commit without losing that file again?</p>
  
  <p>Sorry for the title. I was trying to be descriptive, but ..</p>