Modify functions were broken.

[jorrizza]

Every function that modified LDAP attributes broke. This quickly fixes it. Don't know if it's the right way, but it seems to work for me :)

[halostatue]

The unit tests fail under this change.

 1) Error:
test_modify_ops_add(TestLDAP):
NoMethodError: undefined method `modify_ops' for Net::LDAP::Connection:Class
    ./test/test_ldap_connection.rb:13:in `test_modify_ops_add'

  2) Error:
test_modify_ops_delete(TestLDAP):
NoMethodError: undefined method `modify_ops' for Net::LDAP::Connection:Class
    ./test/test_ldap_connection.rb:6:in `test_modify_ops_delete'

  3) Error:
test_modify_ops_replace(TestLDAP):
NoMethodError: undefined method `modify_ops' for Net::LDAP::Connection:Class
    ./test/test_ldap_connection.rb:20:in `test_modify_ops_replace'

28 tests, 145 assertions, 0 failures, 3 errors
rake aborted!

[halostatue]

I've fixed this and pushed out 0.2.1.