Log Message:
Update to 0.8.

  Don't complain if there is no custom-kernel file, and don't try to
  build GENERIC as the default custom kernel, because it's built
  anyway if appropriate for that port.

  Support .branch to define branch for builds from NetBSD imported
  into a VCS, rather than checked out from NetBSD's CVS.  Example
  contents for .branch is "5\n" for netbsd-5.

  Support local and relative paths in .tree, for placing the obj
  container in arbitrary locations.