Prevent conflicts with Linux dark themes
(and slightly darken calltip background).

Every other menudef key is the lowercase version of the
corresponding main menu entry (in this case, 'Window').

Create a template for minimally testing a tkinter-using module by importing it and instantiating its class(es).  Add a test file for all non-startup IDLE modules.  Edit existing files and update coverage.  This is part 1 of 3, covering the 21 autocomplete to help modules and touching 33 idlelib files.

Before, <return> would not, for instance, complete 're.c' to 're.compile' even with 'compile' highlighted.  Now it does.  Before, <return> was inserted into text, which in Shell meant compile() and possibly execute.  Now cursor is left after completion.

The root problem was non-check for hide_event. When user clicks
on autocomplete window (acw), root widget gets focusOut event, then triggers hide_window to
close the acw. It should only be hide when acw is active, and acw didn't
get focus at FocusOut event (this event bind on acw and widget), or when
widget get a ButtonPress event (this event only bind on widget).

MacOS  froze after double click on acw because when
doubleclick_event try to hide window at the end, hide_window function
destory whole acw, but tkinter didn't get focus back to widget. So set focus
on widget first, then destory acw.

Windows could not respond on double click event, because of the misbehavior
of Configure event.  When acw was shown, tkinter called winconfig
event multiple times.  That caused tkinter to not response to double
click event.  When on Windows, unbind Configure event first
time get into winconfig_event to prevent multiple call of this event.

Fixes problem with writing docstrings at lease twice indented.

In a few cases, reverse a condition and eliminate a return.