- add support for Control syntax;
- use Control syntax and objectIdentifierFirstComponentMatch
  with reqControls/reqRespControls

behave when a value of an ordered attr starts with '{' and either contains or not '}', but the prefix '{X}' does not contain a numericString

Extend ldap_create_control() to supporting creating such.

fix subtree rename integrity; curiously enough, tes023 only failed on 64 bit arch; probably because we'd need to double the stack of the slab on 64 bit archs...