pgsql: Teach the regular expression functions to do case-insensitive

Log Message:
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Teach the regular expression functions to do case-insensitive matching and
locale-dependent character classification properly when the database encoding
is UTF8.

The previous coding worked okay in single-byte encodings, or in any case for
ASCII characters, but failed entirely on multibyte characters. The fix
assumes that the <wctype.h> functions use Unicode code points as the wchar
representation for Unicode, ie, wchar matches pg_wchar.

This is only a partial solution, since we're still stupid about non-ASCII
characters in multibyte encodings other than UTF8. The practical effect
of that is limited, however, since those cases are generally Far Eastern
glyphs for which concepts like case-folding don't apply anyway. Certainly
all or nearly all of the field reports of problems have been about UTF8.
A more general solution would require switching to the platform's wchar
representation for all regex operations; which is possible but would have
substantial disadvantages. Let's try this and see if it's sufficient in
practice.

Modified Files:
--------------
pgsql/src/backend/regex:
regc_locale.c (r1.9 -> r1.10)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/regex/regc_locale.c?r1=1.9&r2=1.10)
pgsql/src/include/regex:
regcustom.h (r1.7 -> r1.8)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/regex/regcustom.h?r1=1.7&r2=1.8)