1009429 - Document the selinux boolean.

https://bugzilla.redhat.com/show_bug.cgi?id=1009429
I think saying apache allows us to be specific and helpful today, and gives us something to grep for when we want to "generalize" it later. I think of generalizing this aspect of our docs as being its own activity, and until "general" is the default I use "specific" as the default. I'm OK with whatever you decide.