Generalising bzr-builder

[Ian Clatworthy]

I started reading the bzr-builder code today. It looks pretty neat.

I've got some code changes and help changes I'll be submitting soon.
I'll also be adding builder to the Plugins Guide. The best place to put
it will depend on whether we generalise it or not so I thought I'd raise
the idea for consideration.

In particular, the "build" command nicely solves a common problem:
building a "tree image" from multiple pieces. As well as building a tree
ready for deb packaging, it looks useful for building QA images for
testing and images for packaging distro packages, Windows installers and
OS X bundles. I wonder if we should generalise it accordingly? At first
glance, it wouldn't take much to do this, e.g. moving the deb-version
clause out of the top line into an optional command, say. Alternatively,
we could put "build" and "dailydeb" into different plugins?

Thoughts?

Ian C.