need to be managed completely by -lldap_r.

	Likely broke things for non-posix threadings....

Update -lldap_r implementation to:
	remove attribute support
	hide thread detachment
	provide concurrency accessors
	provide initialization function
	fix gethostby{addr,name}_r codes (not coverred by HAVE_REENTRANT_FUNCTIONS)
Update servers/libraries to use ldap_pvt_thread_ calls.
Cleanup server codes (no #ifdef HAVE_PTHREAD_THIS or _THATs)!
Removed -llthread

type 'sig_atomic_t' and marked it volatile.  Add detection to
configure to ensure sig_atomic_t and volatile are supported.