Teach regular expression operators to honor collations.

This involves getting the character classification and case-folding
functions in the regex library to use the collations infrastructure.
Most of this work had been done already in connection with the upper/lower
and LIKE logic, so it was a simple matter of transposition.

While at it, split out these functions into a separate source file
regc_pg_locale.c, so that they can be correctly labeled with the Postgres
project's license rather than the Scriptics license.  These functions are
100% Postgres-written code whereas what remains in regc_locale.c is still
mostly not ours, so lumping them both under the same copyright notice was
getting more and more misleading.

src/backend/libpq/hba.c

@@ -25,6 +25,7 @@
 #include <arpa/inet.h>
 #include <unistd.h>
 
+#include "catalog/pg_collation.h"
 #include "libpq/ip.h"
 #include "libpq/libpq.h"
 #include "regex/regex.h"
@@ -1781,7 +1782,7 @@ parse_ident_usermap(List *line, int line_number, const char *usermap_name,
 		 * XXX: Major room for optimization: regexps could be compiled when
 		 * the file is loaded and then re-used in every connection.
 		 */
-		r = pg_regcomp(&re, wstr, wlen, REG_ADVANCED);
+		r = pg_regcomp(&re, wstr, wlen, REG_ADVANCED, C_COLLATION_OID);
 		if (r)
 		{
 			char		errstr[100];