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.

src/include/regex/regcustom.h

@@ -25,7 +25,7 @@
  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- * $PostgreSQL: pgsql/src/include/regex/regcustom.h,v 1.7 2008/02/14 17:33:37 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/regex/regcustom.h,v 1.8 2009/12/01 21:00:24 tgl Exp $
  */
 
 /* headers if any */
@@ -34,6 +34,17 @@
 #include <ctype.h>
 #include <limits.h>
 
+/*
+ * towlower() and friends should be in <wctype.h>, but some pre-C99 systems
+ * declare them in <wchar.h>.
+ */
+#ifdef HAVE_WCHAR_H
+#include <wchar.h>
+#endif
+#ifdef HAVE_WCTYPE_H
+#include <wctype.h>
+#endif
+
 #include "mb/pg_wchar.h"