Synchronize with the following versions of the English version:
preface.sgml 1.29
network.sgml 1.21
serial.sgml 1.4
(I also changed a link in network.sgml to point to the English handbook)
PR: 10686, 10687, 10688
Submitted by: Andrey Zakhvatov <andy@icc.surw.chel.su>