database.php: add deleteScript function
remember last successful LDAP server

cache last successful LDAP server for minimize
LDAP auth delay when primary server is down

queryLDAPServer:
	Try to connect to last successful LDAP server.
	If there is no last successful server, then cycle
	through servers that specified in configuration
	and save found server in cache.

authenticated_via_ldap:
	Invalidate last successful server cache on
	configuration change

authenticated_via_ldap_cache:
	LDAP cache invalidation check was moved to
	authenticated_via_ldap