Build the list of pages only once

[jammon]

Site.pages() reads the list of pages every time it is called. I don't think, that it's meant to be like that.

[krallin]

I think this would break the cactus serve command (@koenbok did most of the work on it, so I'm not sure).

It used to work the way you're describing it, but was changed here: c297ad1

So, I'd avoid merging this for now until Koen can clarify the intention in that change.

Cheers,

[jammon]

Probably you are right. I found a situation (after some more code changes) that a seemingly unrelated test failed, because it relied implicitly on the files being read for every call to site.pages(). Can I take this pull request back?