added simple test to confirm decay works

The epsilon for the half-life decayed comparison might need to be adjusted when we actually get decay to return non-empty CompMaps.  This test should pass for v1.2 - it currently fails - even with @scopatz's `br` branch update.
Correct that this is not true in the general case, but it isn't a general
test - it *should* be true for *this* test.

On Mon, Dec 1, 2014 at 4:34 PM, Anthony Scopatz <notifications@github.com>
wrote:

> In tests/decayer_tests.cc:
>
> > +  v[id("Cs137")] = 1;
> > +  v[id("U238")] = 10;
> > +  cyclus::compmath::Normalize(&v);
> > +
> > +  double secs_per_yr = 3.15569e7;
> > +  double cs_half_life_yr = 30.17;
> > +
> > +  cyclus::Decayer dec(v);
> > +  dec.Decay(secs_per_yr * cs_half_life_yr);  // 2419200 == secs / month
> > +  cyclus::CompMap newv;
> > +  dec.GetResult(newv);
> > +
> > +  cyclus::compmath::Normalize(&newv);
> > +
> > +  ASSERT_TRUE(newv.size() > 0) << "decayed composition has zero nuclides";
> > +  ASSERT_TRUE(newv.size() > v.size()) << "decayed composition should have more nuclides than original";
>
> This is not necessarily true if we drop zero frac species. I don't know if
> we do...
>
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> <https://github.com/cyclus/cyclus/pull/1050/files#r21125616>.
>