'Find in files' by replacing 'open with implicit close' by 'with open' in
GrepDialog method grep_it. Streamline code with enumerate(), direct file
iteration, and output tweak. Add test for this method, including output format.

Problem noted & original patch by Serhiy Storchaka; I tweaked the patch a bit.

http://www.freebsd.org/doc/en/books/arch-handbook/driverbasics-block.html

* state that python3 source encoding is UTF-8, and give examples

* mention surrogateescape in the 'tips and tricks' section, and
  backslashreplace in the "Python's Unicode Support" section.

* Describe Unicode support provided by the re module.

* link to Nick Coghlan's and Ned Batchelder's notes/presentations.

* default filesystem encoding is now UTF-8, not ascii.

* Describe StreamRecoder class.

* update acks section

* remove usage of "I think", "I'm not going to", etc.

* various edits

* remove revision history and original outline

Patch contributed by Corey Brune.

The exception is the import related questions at the end, which
need to be rewritten anyway.

ISO C90 forbids mixed declarations and code

faulthandler._read_null() is not reliable: it does not crash on AIX.

sigwaitinfo() can be interrupted on Linux (raises InterruptedError), but not on
AIX.

when \r\n appears at end of 65535 bytes without other newlines.

* Use mixins for generating tests for different compression types.
* Make test_tarfile discoverable.
* Use more special tests (i.e. assertEqual, assertIs) instead of assertTrue.
* Add explicit test skips instead of reporting skipped tests as passed.
* Wrap long lines.
* Correct a comment for test_hardlink_extraction1.
* Add support.requires_gzip.

and some other minor enhancements.

Also, improve some docstring descriptions of the 'errors' parameter.

Closes #14015.

exec runs into an error.  Prevent a regular multi-close of the /dev/null
fd when any of stdin, stdout and stderr was set to DEVNULL.

Reported by Atsuo Ishimoto.