Must specify protocol for client-uvm sharing of signal handlers

Created by: mn200

As per discussion in meeting on 1 August 2014, we think that the uVM should be the only entity making the signal system call. Other entities (i.e., clients in practice) can register signal-handler-like objects with the uVM, which promises to pass on signals generated by their code.

This needs to be documented in the spec-wiki, perhaps in a section about client-uVM API.