Fix a regression from changeset d544873d62e9 (issue #15989).

Patch by Jeffrey Armstrong.

when result of PyInt_AsLong() or PyLong_AsLong() narrowed
to int without checks.

This is a backport of changesets 13e2e44db99d and 525407d89277.

strings with whitespaces, backslashes or unbalanced braces.

in any mapping, not only in an unicode string.

could be the cause of a random failure).

special characters in the file path.

returns ESRCH for a zombie process, which is not POSIX-compliant.

Now pindent.py works with a "with" statement.  pindent.py no longer produces
improper indentation.  pindent.py now works with continued lines broken after
"class" or "def" keywords and with continuations at the start of line.  Added
regression tests for pindent.py.  Modernized pindent.py.