ITS#5408 part 9 - Sorted RDNs.

ITS#5408 part 9 - Sorted RDNs.
- Parse sorted attrs more carefully:
  Accept only attr={num}val.ldif and attr=val{num}.ldif and only base 10.
  Sort "attr=foo" before "attr=foo{n}".  Truncate at ".ldif" while sorting.
- Make the sort order independent of the LDIF files' order in the directory.