BUILD: Change error message if missing cifsimap.h cifs-idmap plugin is enabled by default, but required header file cifsidmap.h needn't be available on other distributions. It was not clear that cifs-idmap plugin is optional feature of sssd. With this patch, configure will recommend to build sssd without cifs idmap plugin if cifsidmap.h is not available. Resolves: https://fedorahosted.org/sssd/ticket/2125

Add CIFS idmap plugin https://fedorahosted.org/sssd/ticket/1534