Fix import_path for python

[kuba--]

for following python code:

import sys
sys.path.append('/foo/bar/mock-0.3.1')

from testcase import TestCase
from testutils import RunTests
from mock import Mock, sentinel, patch

and command: ./qpl -f /tmp/test.py.pl -f import.pl -q "import_path(Path)."
we get:

Path = [sys,Head]
Path = [testcase]
Path = [testutils]
Path = [mock]

Head atom is incorrect here!