Date profile fields in ldapprov are passed as an array instead of a string

When date profile fields are present in the registration form, the value of a date field passed to LDAP is an array (instead of a string). The date doesn't get written and an error message is displayed. Similar issue for ldapdata is solved here: http://drupal.org/node/171763

This submitted patch is based on the solution provided here: http://drupal.org/node/171763#comment-2153240

And this is the error received when registering users with a date field:
warning: ldap_modify() [function.ldap-modify]: Modify: Invalid syntax in ldap_integration/includes/LDAPInterface.inc on line 260.