Initialize sid_str to NULL to avoid freeing random data

If any function before failed, sss_idmap_free_sid() might have been
called with random data.
Replace prog_DEPENDENCIES with EXTRA_prog_DEPENDENCIES

Automake computes build dependencies of a program automatically but not
if prog_DEPENDENCIES is set. In this case only the dependencies given by
prog_DEPENDENCIES are used. If the automatically calculated dependencies
should be augmented EXTRA_prog_DEPENDENCIES should be used.
BUILD: Explicitly link libsss_ad.so with sasl libs

If openldap is not built with sasl support
libsss_ad.so will not be linked with libsasl2 although
sasl_client_init is called by function ad_sasl_initialize.
BUILD: Use OPENLDAP_CFLAGS instead of LDAP_CFLAGS

LDAP_CFLAGS is never defined.
OPENLDAP_CFLAGS is set by src/external/ldap.m4.

This patch does:
  sed -i 's/$(LDAP_CFLAGS)/$(OPENLDAP_CFLAGS)/' Makefile.am
Add ldap_autofs_map_master_name option
Signals: Remove unused functions

Cleanup unused signal functions
Signals: Remove empty sig_hup

SIGHUP handling is implemented later using a tevent handler so sig_hup() is
useless.
Signals: Refactor termination of processes

sig_term() was never used as a real signal handler, but only called by tevent
signal handlers in the kerberos and ldap children.
Also the same code was duplicated with separate local guard variables in other
functions.
Unify orderly termination handling, between all these functions.
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
Remove unused variable
LDAP: Prevent from using uninitialized sdap_options

ldap_get_options can fail in time of ldap back end initialisation
and then sssd try to release uninitialised sdap_options.

Resolves:
https://fedorahosted.org/sssd/ticket/2147
PAC: Free config attribute when it's processed
cmocka unit test for authtok module added.
added null checks to authtok module
more tests added for authtok module
merged