Explicitly providing tosdir to ncc

Not assuming an environment variable is set.
Explicitly set $TOSROOT in the app Makefile

This removes the non-desireable requirement that a user must set
environment variables in order to build TinyOS. The $TOSROOT variable
then trickles through the makefiles and in makerules $TOSDIR is set.

The overhead to do this is small (1 line in each application makefile)
but it should really help make tinyos more user friendly.
Cleaned up whitespace