pg_dump: Strict names with no matching schema

When using pg_dump --strict-names and a schema pattern which doesn't
match any schemas (eg: --schema='nonexistant*'), we were incorrectly
throwing an error claiming no tables were found when, really, there
were no schemas found:

  -> pg_dump --strict-names --schema='nonexistant*'
  pg_dump: no matching tables were found for pattern "nonexistant*"

Fix that by changing the error message to say 'schemas' instead, since
that is what we are actually complaining about.

Noticed while testing pg_dump error cases.

Back-patch to 9.6 where --strict-names and this error message were
introduced.

src/bin/pg_dump/pg_dump.c

@@ -1216,7 +1216,7 @@ expand_schema_name_patterns(Archive *fout,
 
 		res = ExecuteSqlQuery(fout, query->data, PGRES_TUPLES_OK);
 		if (strict_names && PQntuples(res) == 0)
-			exit_horribly(NULL, "no matching tables were found for pattern \"%s\"\n", cell->val);
+			exit_horribly(NULL, "no matching schemas were found for pattern \"%s\"\n", cell->val);
 
 		for (i = 0; i < PQntuples(res); i++)
 		{