Improve virtualenv support & egg-link resolution

- add sys_path= kwarg to Script & Evaluator constructors

- store sys_path for each evaluator instance

- replace get_sys_path with get_venv_path

- get_venv_path: use addsitedir to load .pth extension files

- get_venv_path: look for egg-link files in all directories in path

test/test_evaluate/test_sys_path.py

@@ -1,4 +1,8 @@
 import os
+from glob import glob
+import sys
+
+import pytest
 
 from jedi._compatibility import unicode
 from jedi.parser import Parser, load_grammar
@@ -19,13 +23,30 @@ def test_paths_from_assignment():
     assert paths('sys.path, other = ["a"], 2') == []
 
 
-def test_get_sys_path(monkeypatch):
-    monkeypatch.setenv('VIRTUAL_ENV', os.path.join(os.path.dirname(__file__),
-                                                   'egg-link', 'venv'))
-    def sitepackages_dir(venv):
-        return os.path.join(venv, 'lib', 'python3.4', 'site-packages')
+# Currently venv site-packages resolution only seeks pythonX.Y/site-packages
+# that belong to the same version as the interpreter to avoid issues with
+# cross-version imports.  "venvs/" dir contains "venv27" and "venv34" that
+# mimic venvs created for py2.7 and py3.4 respectively.  If test runner is
+# invoked with one of those versions, the test below will be run for the
+# matching directory.
+CUR_DIR = os.path.dirname(__file__)
+VENVS = list(glob(os.path.join(CUR_DIR,
+                               'venvs/venv%d%d' % sys.version_info[:2])))
 
-    monkeypatch.setattr('jedi.evaluate.sys_path._get_venv_sitepackages',
-                        sitepackages_dir)
 
-    assert '/path/from/egg-link' in sys_path.get_sys_path()
+@pytest.mark.parametrize('venv', VENVS)
+def test_get_venv_path(venv):
+    pjoin = os.path.join
+    venv_path = sys_path.get_venv_path(venv)
+
+    site_pkgs = (glob(pjoin(venv, 'lib', 'python*', 'site-packages')) +
+                 glob(pjoin(venv, 'lib', 'site-packages')))[0]
+    ETALON = [
+        site_pkgs,
+        pjoin(site_pkgs, '.', 'relative', 'egg-link', 'path'),
+        pjoin('/path', 'from', 'egg-link'),
+        pjoin(site_pkgs, 'dir-from-foo-pth'),
+        pjoin('/path', 'from', 'smth.py'),
+        pjoin('/path', 'from', 'smth.py:extend_path')
+    ]
+    assert venv_path[:len(ETALON)] == ETALON