improve timeout support (ITS#4157, ITS#4663); manpage cleanup

doc/man/man5/slapd-ldap.5

servers/slapd/back-ldap/add.c

servers/slapd/back-ldap/back-ldap.h

servers/slapd/back-ldap/bind.c

servers/slapd/back-ldap/chain.c

servers/slapd/back-ldap/compare.c

servers/slapd/back-ldap/config.c

servers/slapd/back-ldap/delete.c

servers/slapd/back-ldap/distproc.c

servers/slapd/back-ldap/modify.c

servers/slapd/back-ldap/modrdn.c

servers/slapd/back-ldap/search.c