This is an unfinished blog idea.

build products: come from some build script
normally unversioned/ignored from VCS
in some cases pretty useful:
  * generated PDF files from latex sources
  * autotools generated Makefile.in/Makefiles.

bzr plugin that tracks unversioned files

special handling in case of conflicts: regenerate
i.e. bzr needs to know how to regenerate them

reference to continous integration builds like in aegis