Code review comment for lp://staging/~benji/python-pgbouncer/buildout-fixes-and-tweaks

> *ALL* our projects use those shared cache directories. What benefit does
> making it harder for the 99% of contributors that also work on other LP stuff
> serve?

We don't specify them in MAAS. Instead we expect people to create
their own in ~/.buildout (see HACKING.txt). It's less surprising to
omit them from buildout.cfg, because then anyone can build the project
without wondering what's going on:

{{{
While:
  Initializing.
Error: The specified download cache:
'/home/gavin/Launchpad/python-pgbouncer/trunk/download-cache'
Doesn't exist.
}}}

Specifying them makes the project harder to start with for casual
contributors, and probably for some not-so-casual contributors.

In places where we must use the cache, the following would have the
desired effect:

  $ ./bootstrap.py buildout:download-cache=download-cache buildout:eggs=eggs
  $ ./bin/buildout buildout:download-cache=download-cache buildout:eggs=eggs