Log Message:
Updated pcre2 to 10.23.

Version 10.23 14-February-2017
------------------------------

1. ChangeLog has the details of a lot of bug fixes and tidies.

2. There has been a major re-factoring of the pcre2_compile.c file. Most syntax
checking is now done in the pre-pass that identifies capturing groups. This has
reduced the amount of duplication and made the code tidier. While doing this,
some minor bugs and Perl incompatibilities were fixed (see ChangeLog for
details.)

3. Back references are now permitted in lookbehind assertions when there are
no duplicated group numbers (that is, (?| has not been used), and, if the
reference is by name, there is only one group of that name. The referenced
group must, of course be of fixed length.

4. \g{+<number>} (e.g. \g{+2} ) is now supported. It is a "forward back
reference" and can be useful in repetitions (compare \g{-<number>} ). \ 
Perl does
not recognize this syntax.

5. pcre2grep now automatically expands its buffer up to a maximum set by
--max-buffer-size.

6. The -t option (grand total) has been added to pcre2grep.

7. A new function called pcre2_code_copy_with_tables() exists to copy a
compiled pattern along with a private copy of the character tables that is
uses.

8. A user supplied a number of patches to upgrade pcre2grep under Windows and
tidy the code.

9. Several updates have been made to pcre2test and test scripts (see
ChangeLog).