Fix some minor grammar and punctuation problems.
freebsd-update: change one mention to a man entity.
freebsd-update: Set SRCCONF to null in both custom kernel sections.
doc: add link to FDP in "building doc from source" section.
doc: use <replaceable> in svn URL
Move indexterm in signal 11 FAQ to answer fix rendering.
Some changes suggested by Mehmet Erol Sanliturk
<m.e.sanliturk@gmail.com>.