Issue #18760: Improved cross-references in the xml package.
Issue #18743: Fix references to non-existant "StringIO" module
in docstrings and comments.
Issue #18643: Fix some test_socket failures due to large default socket buffer
sizes.
Merge.
Fixes issue #15507: test_subprocess's test_send_signal could fail if the test
runner were run in an environment where the process inherited an ignore
setting for SIGINT.  Restore the SIGINT handler to the desired
KeyboardInterrupt raising one during that test.