Definition of slapd pid and args files as slapd.conf general parameters;

Definition of slapd pid and args files as slapd.conf general parameters;
introduction of pid/agrs parameters to the test-suite slapd.conf files;
creation of sub-directory test/var for storage of pid/args files during test;
update of the slapd and slapd.conf man pages.
(The change reduces dependency on ldapconfig.h, since SLAPD_PIDEXT
 and SLAPD_ARGSEXT are deleted from the code.)