FreeBSD/doc 5e98483 (r52948)en_US.ISO8859-1/books/porters-handbook/versions chapter.xml

Document OSVERSIONs 1300019 and 1300020.

Add an internal comment that OSVERSION 1300021 existing but only for the
space of 9 commits.
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+21-0en_US.ISO8859-1/books/porters-handbook/versions/chapter.xml
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