Issue #8260: The read(), readline() and readlines() methods of
codecs.StreamReader returned incomplete data when were called after
readline() or read(size).  Based on patch by Amaury Forgeot d'Arc.
Issue #19990: Added tests for the imghdr module.
Based on patch by Claudiu Popa.
Issue #20338: Increase allowed tip width slightly and wrap long signagure lines.
Original patch by Serhiy Storchaka.
Merge heads.
Idlelib.calltips: add test of starred first parameters. They should not be
removed even for bound methods. (Inspect.signature does, see 20401.)
Issue #17721: Remove non-functional configuration dialog help button until we
make it actually gives some help when clicked. Patch by Guilherme Simões.
eliminate redundancy between yield stmt and yield expr docs (closes #12704)

Patch by Nikolaus Rath.