remove support for compiling on systems without getcwd()

Do we need a fallback implementation of getcwd() from 1991 that claims to
support "really old Unix systems"? I don't think so.
test_socket: cancel scheduled alarm on test failure
(Merge 3.3) test_socket: cancel scheduled alarm on test failure
Close #18538: ``python -m dis`` now uses argparse.

Patch by Michele Orr?.
Issue #18756: make test_urandom_failure more robust by executing its code in a subprocess
Issue #18756: make test_urandom_failure more robust by executing its code in a subprocess
Issue #18772: fix the gdb plugin after the set implementation changes
Various clarifications based on feedback & questions over the years.
(grafted from 23181bf411a16287a0a54e910fc0f9ecd2764bf0)
Various clarifications based on feedback & questions over the years.
Clarify the documentation of XMLParser.close

The return value of close() is not always a toplevel element. It depends on
what the underlying target returns. By default, TreeBuilder returns the
toplevel document element.