title: Best way to find (a) buggy file(s) with git
body: <p>I wonder if any of you have a good method finding the "bad file/code".
  Let's say we have a branch from a working master. I change several files (+10).
  After the change I discover that something broke, and let's for arguments sake state it is not an obvious error.
  When stashing my changes - it works.
  Popping the back the changes - broken.</p>
  
  <p>I know I can use git diff, which is excellent, but that means I have to understand all the implications of a specific change (and in a legacy system you didn't build that is more often then not the case). And for 10+ files it tend to get boooring - and we don't want boring, do we?</p>
  
  <p>I was pondering about a way to stash only specific files - is that possible?</p>
  
  <p>Or perhaps to make a copy of the branch and "checkout --" the files one by one?</p>
  
  <p>How would you do?</p>