Attempts to find the #Dependency on the system. Returns the filename of the
  native library or None if it can not be found.

def resolve_dependency(dep):
  """
  Attempts to find the #Dependency on the system. Returns the filename of the
  native library or None if it can not be found.
  """

  for dirname in os.getenv('PATH', '').split(os.pathsep):
    filename = os.path.join(dirname, dep.name)
    if os.path.isfile(filename):
      return _get_long_path_name(filename)
  return None