Inline documentation for hooks in wp-admin/includes/menu.php.

Also fixes syntax for a few unrelated multi-line comments in the file.

Props kpdesign for some minor cleanup.
Fixes #27430.

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git-svn-id: http://core.svn.wordpress.org/trunk@27513 1a063a9b-81f0-0310-95a4-ce76da25c4cd