[OE-core] [PATCH] Add support for remote layering.

[Jeremy Puhlman]

> * Maybe need to split into "bootstrap" steps (e.g where pseduo is
   established, layers downloaded etc)

 So for the most part, the last product we shipped was largely arranged
in this manner. We were using collections, but in many cases layers is
just a reimplementation at a lower level(which is definitely goodness).
During ELC I had a number of discussions primarily around remote layer
fetch and most of the responses were meh, or that they wanted to make
the tool external to bitbake. So after the conference was over I went
ahead and worked out a version of the implementation  that could be done
either in a include or in the bitbake code itself. The version in the
git repo below is obviously just the bitbake implementation.

I have a rough implementation largely based off of collection.inc + some
enhancements we made internally for remote collection fetching. Some of
it is messy(setting up the early fetching vars with out using another
config), but for the ones I list in the patch header it appears to work
well.

I do not believe that this is complete, but it is probably a reasonable
starting point.

Pull URL: git://gitorious.org/jpwork/bb.git
Branch: remote-layering
Browse: https://gitorious.org/jpwork/bb/trees/remote-layering