in poplib, limit maximum line length that we read from the network (closes #16041)

Patch from Berker Peksag.
smtplib: limit amount read from the network (closes #16042)
add a default limit for the amount of data xmlrpclib.gzip_decode will return (closes #16043)
merge 2.7.9 release branch
Issue #16893: Update Idle doc chapter to match current Idle and add new
information.
Update idlelib/NEWS.txt.