makefile_engine package info: Fix vendor
Add target for building a Haiku package repository

* Add rule HaikuRepository to build a repository from a repository info
  file and a list of package files. It calls a build_haiku_repository
  script which does all the work.
* Add target <repository>haiku for building the Haiku package
repository.
  It should be built via "jam -q @alpha-raw build <repository>haiku";
  the build profile is only needed to activate all build features.