use ldap_pvt_ routines (replacing old lthread impl)

	shutdown without busy loop, explicit yield func no longer mandatory
	use pthread_detach() to detach threads (instead of creating them
		in a detached state)
	pthread_create error reporting
	moved declarations to init.c
Import configure changes:
	revamp res_search check
	remove strtok_r check

to add a simple mutex.  Should be two (proto-slap.h & init.c).

Includes everything but ldapext & ldap.conf changes.