v0.2.4

Four defects reported by Raivo Hool, who has been carrying patches for
this module in his own tree for years. His commits are rebuilt against
this fork, which had moved too far for them to apply.

Fixed

• A client that went away in the middle of an authentication left its
  request linked into the server's waiting queue, and the LDAP connection
  it held was never given back. The next connection returned to the pool
  walked into that node and woke a request whose pool was gone. A pool
  cleanup handler now returns the connection and unlinks the node.
• request_timeout was armed on the client connection's write event,
  whose handler belongs to nginx core, so it was noticed only when the
  phase handler happened to re-enter. It is a timer of its own now.
• An empty user name went into the LDAP search, where it produces a
  filter matching an entry whose attribute is empty. It is answered with
  401, as an empty password already was.
• auth_ldap_cache_size above 8872 entries was silently reduced to that.
  The bucket table reaches 32632 entries now, and a size that still does
  not fit is reported instead of being capped without a word.