Merge the following from the English version:
1.249 -> 1.256 handbook/ports/chapter.sgml
Submitted by: Ryusuke Suzuki <ryusuke _at_ jp dot FreeBSD dot org>
Reviewed by: Hiroo Ono <hiroo _at_ jp dot FreeBSD dot org>
References: [doc-jp-work 1790, 1811, 1813, 1814]