title: Git merge of same and externally modified file
body: <p>I have inherited some code (from zip file) from a developer and git
  initialzed, made changes and set of check-ins progressively.</p>
  
  <p>Now, the same developer released the same code with his changes and gave me the
  another zip file. </p>
  
  <p>How do i merge my changes which i have it my git repo and his recent changes 
  from the second zip file contents?</p>
  
  <p>Ideally, i would like to have the code which should be accumalation of both
  my changes and the developer recent changes.</p>
  
  <p>I tried to create branch b1 from my master branch and applied second zip file contents on top of that. committed those files in the branch and did 'git checkout master; git merge b1' - but, i do not get my changes, only his changes in my master branch.</p>