Backport PR #4086: fix missing errno import

trivial fix, this import was missing, but it's only triggered when there's a
race condition, which is why this hasn't come up.

IPython/core/profiledir.py

@@ -23,6 +23,7 b' Authors:'
 
 import os
 import shutil
+import errno
 
 from IPython.config.configurable import LoggingConfigurable
 from IPython.utils.path import get_ipython_package_dir, expand_path