Returns a client connection to the specified LDAP URL. If a bind
DN is specified (either through a "bindname" extension in
ldap_url or, if there isn't one, through binddn ) then the
connection will be bound using that DN and the optional password.
If no bind DN is given then any connection is returned, regardless
of the bind DN it is using.
version may be used to specify the required protocol version in
the bind operation. If zero or left out, a bind attempt with the
default version (currently 3) is done with a fallback to
2 if that fails. Also, a cached connection for any version
might be returned if version isn't specified.
As opposed to creating an Protocols.LDAP.client instance
directly, this function can return an already established
connection for the same URL, provided connections are given back
using return_connection when they aren't used anymore.
A client object with an error condition is returned if there's a
bind error, e.g. invalid password.
Protocols.LDAP.get_cached_filter()