IDLE squeezer: improve unsqueezing and autosqueeze default

GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2019-01-30.03:14:30.153>
labels = ['3.8', 'expert-IDLE', 'type-feature', '3.7', '3.9']
title = 'IDLE squeezer: improve unsqueezing and autosqueeze default'
updated_at = <Date 2019-08-25.06:00:37.543>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2019-08-25.06:00:37.543>
actor = 'taleinat'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2019-01-30.03:14:30.153>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 35855
keywords = []
message_count = 7.0
messages = ['334541', '334631', '349058', '349066', '349072', '349475', '350429']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'taleinat']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue35855'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']