- Fix release notes build on releng/9.1 [1]

- Fix release notes build on releng/9.1 [1]
- MFC r240508, r240516, r240519 (gabor):
  o Update releng/9.1/release/doc files post-XML conversion.
  o This commit fixes most of the 9-STABLE release build problems.
- Close colspec tags to conform to XML standards. [1]
- Convert installation article to XML stanards. [1]

[1] - These are direct commits to releng/9.1

Approved by:	re (hrs)

git-svn-id: svn://svn.freebsd.org/base/releng/9.1@240710 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f