added new setting LDAP_YUBIKEY_ATTRIBUTE
implemented yubikey from ldap
cleaned previous commits, added ldap_yubikey_attr feature to client API
correcting few implementation bugs for ldap_yubikey_attr feature
ldap scope changed for yubikey attribute searching
fixing typo
Merge pull request #2 from Korrigan/master

[FEATURE] Searching for yubikeys in LDAP