The Code Context menu item only works on Editor windows so disable it for others.

The Code Context menu label now toggles between Show/Hide Code Context. 
 The Zoom Height menu now toggles between Zoom/Restore Height. 
 Zoom Height has moved from the Window menu to the Options menu. 

 
https://bugs.python.org/issue22703

* bpo-34864: warn if "Prefer tabs when opening documents" set to "Always"

* add NEWS entry

* address code review comments

* address second code review comments

* Add entry for idlelib/NEWS.txt.

Fix typos

On Windows 8.1+ or 10, with DPI compatibility properties of the Python binary
unchanged, and a monitor resolution greater than 96 DPI, this should
make text and lines sharper. It should otherwise have no effect.

Using a magnifier, I determined that the improvement comes from horizontal and
lines being better lined up with the monitor pixels. I checked that this call causes
no problem on any Windows buildbot, including the Win7 buildbots. Unlike most
IDLE patches, this one can be easily reverted by users by removing a few lines,
at the top of idlelib/pyshell.py.

Patches are in 3.7.0a3 even if this update is not.

Reformat a few early 3.x entries in HEWS.txt.