bpo-29512: Rename Lib/test/bisect.py to bisect_cmd.py (#7229)

Rename Lib/test/bisect.py to Lib/test/bisect_cmd.py. The old name was
in conflict with Lib/bisect.py, causing test failures, depending how
tests were run.

For example, "python2.7 Lib/test/test_httpservers.py" imported
indirectly Lib/test/bisect.py instead of Lib/bisect.py
on "import bisect".

Author: vstinner

Lib/test/bisect.py renamed to Lib/test/bisect_cmd.py

@@ -0,0 +1,3 @@
+Rename Lib/test/bisect.py to Lib/test/bisect_cmd.py. The old name was in
+conflict with Lib/bisect.py, causing test failures, depending how tests
+were run.