libwbclient: SSSD implementation This patch implements the libwbclient API for Samba daemons and utilities. The main purpose is to map Active Directory users and groups identified by their SID to POSIX users and groups identified by their POSIX UIDs and GIDs respectively. The API is not fully implemented because SSSD does not support some AD features like WINS or NTLM. Additionally this implementation has its focus on the file-server use case and hence does not implement some features which might be needed for a domain controller use case. Some API calls are generic and independent of the backend like e.g. converting binary SIDs and GUIDs into a string representation and back or memory allocation and deallocation. These parts are taken from the original Samba sources together with copyright and authors. Files with'_sssd' as part of the name contain the SSSD related calls. Resolves: https://fedorahosted.org/sssd/ticket/1588 Reviewed-by: Jakub Hrozek <jhrozek@redhat.com> Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>