[IPA] Attribute dereferencing & storing SID as string

[Endi Sukma Dewata]

Andrew,

I've modified the patches based on your advice. I also added another
patch for resolving conflicts between AD schema and standard LDAP
schema, which is a requirement for using the sambaSID attribute.

Please take a look at the attached patches. These are the
corresponding wiki pages:

http://www.freeipa.org/page/Samba_4_Attribute_Dereferencing
http://www.freeipa.org/page/Samba_4_Schema_Mapping
http://www.freeipa.org/page/Samba_4_Storing_SID_in_String_Format

Thanks!

--
Endi S. Dewata