in Auth_with_ldap.pm try binding with user password or compare

in Auth_with_ldap.pm try binding with user password or compare

This changes the checkpw code in Auth_with_ldap.  Along with comparing
the user entered password against the directory attibute userPassword
you can try to bind with the users dn and password.

This is controlled by the option auth_by_bind, which, if set, causes
this code to try binding instead of comparing.

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
Signed-off-by: Henri-Damien LAURENT <henridamien.laurent@biblibre.com>