Issue #27487: Merge runpy warning from 3.5

diff --cc Lib/runpy.py
Simple merge

diff --cc Lib/test/test_cmd_line_script.py
Simple merge

diff --cc Misc/NEWS
index 13e7f3640336dd757f5e3454361d7dc0a8986317,1ecb6f1f94fff49efb501353f459c0bdb5ae3275..ea4aa3fce0238330b689a10a664aa941098d5c96
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -10,9 -10,10 +10,13 @@@ What's New in Python 3.6.0 beta 
  Core and Builtins
  -----------------
  
+ - Issue #27487: Warn if a submodule argument to "python -m" or
+   runpy.run_module() is found in sys.modules after parent packages are
+   imported, but before the submodule is executed.
+ 
 +- Issue #27157: Make only type() itself accept the one-argument form.
 +  Patch by Eryk Sun and Emanuel Barry.
 +
  - Issue #27558: Fix a SystemError in the implementation of "raise" statement.
    In a brand new thread, raise a RuntimeError since there is no active
    exception to reraise. Patch written by Xiang Zhang.