bpo-30843: regrtest fixes sys.path, restore test.bisect (#2567)

* Rename again Lib/test/bisectcmd.py to Lib/test/bisect.py
* regrtest now removes '' and Lib/test/ from sys.path
* Use absolute import in test_bisect

Lib/test/regrtest.py

@@ -464,6 +464,14 @@ def main(tests=None, testdir=None, verbose=0, quiet=False,
         # to locate tests
         sys.path.insert(0, testdir)
 
+    # Make sure that '' and Lib/test/ are not in sys.path
+    regrtest_dir = os.path.abspath(os.path.dirname(__file__))
+    for path in ('', regrtest_dir):
+        try:
+            sys.path.remove(path)
+        except ValueError:
+            pass
+
     if slaveargs is not None:
         args, kwargs = json.loads(slaveargs)
         if kwargs['huntrleaks']:

Lib/test/test_bisect.py

+from __future__ import absolute_import
 import sys
 import unittest
 from test import test_support