title: pycallgraph with pycharm does not work
body: <p>I'm using mac os x and trying to setup pycallgraph.<br>
  Ive installed pycallgraph with pip and graphviz with homebrew.<br>
  Everything works from shell. 
  But not from pycharm. </p>
  
  <pre><code>from pycallgraph import PyCallGraph
  from pycallgraph import Config
  from pycallgraph import GlobbingFilter
  from pycallgraph.output import GraphvizOutput
  
  
  config = Config()
  config.trace_filter = GlobbingFilter(exclude=[
       'pycallgraph.*',
  ])
  
  graphviz = GraphvizOutput(output_file='filter_exclude.png')
  
  with PyCallGraph(output=graphviz, config=config):
      def my_fun(): 
          print "HELLO"
      my_fun()
  </code></pre>
  
  <hr>
  
  <pre><code>/Users/user/Projects/py27/bin/python /Users/user/Projects/py27_django/test2.py
  Traceback (most recent call last):
    File "/Users/user/Projects/py27_django/test2.py", line 15, in &lt;module&gt;
      with PyCallGraph(output=graphviz, config=config):
    File "/Users/user/Projects/py27/lib/python2.7/site-packages/pycallgraph/pycallgraph.py", line 32, in __init__
      self.reset()
    File "/Users/user/Projects/py27/lib/python2.7/site-packages/pycallgraph/pycallgraph.py", line 53, in reset
      self.prepare_output(output)
    File "/Users/user/Projects/py27/lib/python2.7/site-packages/pycallgraph/pycallgraph.py", line 97, in prepare_output
      output.sanity_check()
    File "/Users/user/Projects/py27/lib/python2.7/site-packages/pycallgraph/output/graphviz.py", line 63, in sanity_check
      self.ensure_binary(self.tool)
    File "/Users/user/Projects/py27/lib/python2.7/site-packages/pycallgraph/output/output.py", line 96, in ensure_binary
      'The command "{}" is required to be in your path.'.format(cmd))
  pycallgraph.exceptions.PyCallGraphException: The command "dot" is required to be in your path.
  
  Process finished with exit code 1
  </code></pre>
  
  <hr>
  
  <p>Here:<br>
  <code>/Users/user/Projects/py27/</code> -> virtualenv dir<br>
  <code>/Users/user/Projects/py27_django/</code> -> project dir  </p>
  
  <hr>
  
  <p>What does it want from me?</p>