libnfsidmap: Use public plugin header file if available libnfsidmap was merged with nfs-utils in 2.1.2-rc7. We used private internal interface but required internal functions were dropped in nfs-utils-2.3.1. We need to use newly available public interface. Reviewed-by: Pavel Březina <pbrezina@redhat.com> Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>

AUTOCONF: Update detection of libnfsidmap Reviewed-by: Michal Židek <mzidek@redhat.com> Reviewed-by: Roland Mainz <rmainz@redhat.com>

NFSv4 client: add to build system Reviewed-by: Jakub Hrozek <jhrozek@redhat.com> Reviewed-by: Roland Mainz <rmainz@redhat.com>