Merge the following from the English version.

• Move <indexterm>...</indexterm> to the right place.
• Add missing line.
• Whitespace cleanup.

1.457 -> 1.464 handbook/mirrors/chapter.sgml

Submitted by: Ryusuke Suzuki <ryusuke _at_ jp dot FreeBSD dot org>
References: [doc-jp-work 1937, 1939, 1940, 1944, 1949, 1958]