Revert "Change t_mosfet to remember node id instead of ptr"

Revert "Change t_mosfet to remember node id instead of ptr"

This reverts commit d03a1205f99244550c784b4c8c2694ae643f0278.
The commit was not thought through as it should. In addition it contains
some minor changes that should be recommited - that's why I should do
small commits that tend to a single problem/feature.