router_ldapauth plugin with simple bind support

No SASL support, docs are spare and I couldn't get all the needed pieces, simple binds should work for most use cases

```
plugins = router_ldapauth
route = ^/a ldapauth:LDAP realm,url=ldap://ldap.domain,com;basedn=ou=users,dc=domain.com;binddn=uid=proxy,dc=domain,dc=com;bindpw=password
```

binddn and bindpw can be skipped if LDAP server allows anonymous searches

user can set filter with ```filter=``` (defaults to objectClass=*) and login attribute with ```attr=``` (defaults to uid)

it also uses deprecated API since they are still present (at least under ubuntu 10.04) and it saves me from a lot of #ifdef 

please review