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/regex/regexec.c

@@ -192,6 +192,9 @@ pg_regexec(regex_t *re,
 	if (re->re_csize != sizeof(chr))
 		return REG_MIXED;
 
+	/* Initialize locale-dependent support */
+	pg_set_regex_collation(re->re_collation);
+
 	/* setup */
 	v->re = re;
 	v->g = (struct guts *) re->re_guts;