Global decay off

This implements an optional flag that allows the user to disable the material class' Decay function. This is intended to fix issue #984 which complains of an inability to globally turn off decay (at the very least)

As we discussed before on a development call, this feature simply adds the option to allow or specifically not allow the use of the Decay function in the material class.

Further granularity of options or implementation of global decay was not supposed to be part of this quick fix. In the future, this work can be extended to re-implement the feature in which decay occurs whenever a material composition is queried. However, that implementation of global decay was supposed be left up to further discussion on what folks decide was the best course of action.

This PR focuses on adding the decay flag to the SimInfo object and using that flag in the material class' decay function. 

On Tue, Sep 2, 2014 at 2:53 PM, Anthony Scopatz <notifications@github.com>
wrote:

> In src/context.h:
>
> >            std::string handle = "");
> >
> >    SimInfo(int dur, boost::uuids::uuid parent_sim,
> >            int branch_time, std::string parent_type,
> > -          std::string handle = "");
> > +          bool d = true, std::string handle = "");
>
>  The immediately adjacent handle argument has a default value. Why is
> that allowed, but not this one?
>
> This is a style guide change that we realized only a few months ago and a
> sentence I wish @gidden <https://github.com/gidden> had never read :) We
> are phasing it in gradually.
>
Can I just unread it? Do I have enough saplings for that? =p

> —
> Reply to this email directly or view it on GitHub
> <https://github.com/cyclus/cyclus/pull/995/files#r17011155>.
>



-- 
Matthew Gidden
Ph.D. Candidate, Nuclear Engineering
The University of Wisconsin -- Madison
Ph. 225.892.3192