packaging: clean up

o INSTALLDIR had an extraneous '/' at the end.  remove.
  (functions-build.sh)

o remove extraneous 'cd ${BUILD_ROOT}'s from build.sh.  fixed
  installto so no longer needed.
packaging/tinyos-tools-15: add 1.5.0 for dev trunk

tinyos-tools-1.5.0 (tinyos-tools-15) supports the development trunk
after 6dc714b and prior to bringing in issue #190.  This is the
changes that rippled from .platform changing to platfom.

closes #291