fix #266: return multi-valued attributes from LDAP
fix #266: return multi-valued attributes from LDAP

So the source attribute value can now be:
* `None` if there was no value
* a string (if there was one value)
* a list of strings (if there was more than one value)

adobe-apiplatform/user-sync.py,adorton-adobe/user-sync.py,adorton-adobe/user-sync.py,adobe-apiplatform/user-sync.py