bpo-35755: Remove current directory from posixpath.defpath (GH-11586)

Document the change in a NEWS entry of the Security category.

Lib/posixpath.py

@@ -18,7 +18,7 @@
 extsep = '.'
 sep = '/'
 pathsep = ':'
-defpath = ':/bin:/usr/bin'
+defpath = '/bin:/usr/bin'
 altsep = None
 devnull = '/dev/null'
 

Misc/NEWS.d/next/Security/2019-01-17-10-03-48.bpo-35755.GmllIs.rst

+:func:`shutil.which` now uses ``os.confstr("CS_PATH")`` if available and if the
+:envvar:`PATH` environment variable is not set. Remove also the current
+directory from :data:`posixpath.defpath`. On Unix, :func:`shutil.which` and the
+:mod:`subprocess` module no longer search the executable in the current
+directory if the :envvar:`PATH` environment variable is not set.