title: git executable not found in python
body: <p>I was trying to clone a git repo with access key, but when I am trying to run it, It throws an exception saying git executable not found.
  But i have installed git and the in_it.py shows correct path "C:\Program Files\Git\bin" Also I have installed gitpython to use the library in python </p>
  
  <p>here's my code...</p>
  
  <pre><code>import git
  
  git.Git("D:/madhav/myrep/").clone("@github.com:myrepo/scripts")
  </code></pre>
  
  <p>========= and it throws the following exception =================</p>
  
  <pre><code>Traceback (most recent call last):   File
  "C:\Users\1096506\Desktop\gitclone.py", line 1, in &lt;module&gt;
      from git import Repo   File "C:\Users\1096506\AppData\Local\Programs\Python\Python36-32\lib\site-packages\git\__init__.py",
  line 84, in &lt;module&gt;
      refresh()   File "C:\Users\1096506\AppData\Local\Programs\Python\Python36-32\lib\site-packages\git\__init__.py",
  line 73, in refresh
      if not Git.refresh(path=path):   File "C:\Users\1096506\AppData\Local\Programs\Python\Python36-32\lib\site-packages\git\cmd.py",
  line 293, in refresh
      raise ImportError(err) ImportError: Bad git executable. The git executable must be specified in one of the following ways:
       - be included in your $PATH
       - be set via $GIT_PYTHON_GIT_EXECUTABLE
       - explicitly set via git.refresh()
  
  All git commands will error until this is rectified.
  
  This initial warning can be silenced or aggravated in the future by setting the
  $GIT_PYTHON_REFRESH environment variable. Use one of the following values:
      - quiet|q|silence|s|none|n|0: for no warning or exception
      - warn|w|warning|1: for a printed warning
      - error|e|raise|r|2: for a raised exception
  
  Example:
      export GIT_PYTHON_REFRESH=quiet
  </code></pre>