packaging/tinyos-tools: update comments about how tinyos-tools is built.

In particular what kind of dependencies tinyos-tools has.
packaging/tinyos-tools: make tinyos-tools-15 (devel) package version use SHA

Development trunk builds get packaged using the SHA of the tip of the current
branch as the package version.   Makes it abundently clear that the package
is dependent on the current state of the trunk.