[ejabberd] LDAP improvements

[Evgeniy Khramtsov]

I did some improvements in ejabberd_auth_ldap.erl and mod_vcard_ldap.erl.
The result is:

1. Support for RFC-2254 LDAP filter and UID attribute format.
2. Custom search xdata-form for mod_vcard_ldap.
3. Custom ldap-to-vcard mapping.
3. mod_vcard_ldap doesn't depend on auth method.
4. Virtual hosting support.
5. Compatibility with old configuration file.

Refer to http://re.jabber.ru/~xram for more information.