Log Message:
Update buildtool to 0.8.

Changes in 0.8, state: alpha
----------------------------

    * Full  rewrite  of Buildtool's  own  build  system, which  should
      improve maintenance and portability.

    * New module bt_install, which provides a portable install program
      to not depend on specific system details to do installation.

    * New pthread.subr module  for bt_config, which provides functions
      for  automatic detection  of  a pthreads  implementation in  the
      current system.

    * Added checks  in bt_config: bt_check_func, to  check for generic
      functions (not  specific to any library),  and bt_check_type, to
      check for the presence of a generic type.

    * Fixes in  bt_config's loadable  module support. It  was severely
      broken in the previous version.