Icon author: Andrew Clover, bpo-1490384

Inspect.signature failed on the test case because its isinstance call raised.

Change 0/1 assignments to 'executing', 'canceled', 'reading', 'endoffile'.
These are not used outside of pyshell. Other bools already use False/True.
Add comment about int needed for Windows call.
Remove self.more, unused in idlelib and code.InteractiveInterpreter.
The latter uses 'more' as a local.

Replace tkinter tkSimpleDialog.askinteger with a standard IDLE query dialog.
The new box checks for positivity before returning.

Move required blanking of error text to non-overridden entry_ok().
(Omit news item.)

Since clicking to get an IDLE context menu moves the cursor,
any text selection should be and now is cleared.

It appears standard that moving the text insert cursor away from a selection clears the
selection.  Clearing prevents accidental deletion of a possibly off-screen bit of text.
The update is for Ln and Col on the status bar.

Previously, the button-up part of selecting with a mouse was treated as a click
that meant 'jump' to this line, which modified the context and undid the selection

Test when find_good_parse_start should return 0.

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>