Since PEP 393 in Python 3.3, this value is always 0x10ffff, the
maximum codepoint in Unicode; there's no longer such a thing as a
UCS-2 build of Python, which couldn't properly represent some
characters.

There are a couple of spots left where we still condition on the value
of this constant.  Take them out.

This is the converse of GH-15353 -- in addition to plenty of
scripts in the tree that are marked with the executable bit
(and so can be directly executed), there are a few that have
a leading `#!` which could let them be executed, but it doesn't
do anything because they don't have the executable bit set.

Here's a command which finds such files and marks them.  The
first line finds files in the tree with a `#!` line *anywhere*;
the next-to-last step checks that the *first* line is actually of
that form.  In between we filter out files that already have the
bit set, and some files that are meant as fragments to be
consumed by one or another kind of preprocessor.

    $ git grep -l '^#!' \
      | grep -vxFf <( \
          git ls-files --stage \
          | perl -lane 'print $F[3] if (!/^100644/)' \
        ) \
      | grep -ve '\.in$' -e '^Doc/includes/' \
      | while read f; do
          head -c2 "$f" | grep -qxF '#!' \
          && chmod a+x "$f"; \
        done

Add flag -k to pathscript.py script: preserve shebang flags.

Much like the lower-level logic in commit ef2af1ad4, we had
4 copies of this logic, written in a couple of different ways.
They're all implementing the same standard, so write it just once.

The `expand` option was introduced in 2000 in commit fad27aee1.
It appears to have been always set since it was committed, and
what it does is tell the code to do something essential.  So,
just always do that, and cut the option.

Also cut the `linebreakprops` option, which isn't consulted anymore.