Add support for fmincon options in NonlinearProgram

Now you can do things like:

```
nlp = nlp.setSolverOptions('fmincon', 'Algorithm', 'active-set');
```
ok, great.  didn’t realize we already had the fmincon options, just not the set method.  :)
On Aug 19, 2014, at 5:16 PM, Robin Deits <notifications@github.com> wrote:

> In solvers/NonlinearProgram.m:
> 
> > @@ -377,7 +377,7 @@
> >            obj.solver_options.snopt.LinesearchTolerance = optionval;
> >          end
> >        elseif(strcmpi((solver),'fmincon'))
> > -        error('Not implemented yet');
> > +        obj.solver_options.fmincon = optimset(obj.solver_options.fmincon, optionname, optionval);
> We do, but it's not clear that we do (actually, this is exactly because of the eval(x) vs. x.eval() discussion we had today). NonlinearProgram.solve() calls fmincon(obj,x0), but this is actually a call to NonlinearProgram.fmincon(), which passes the obj.solver_options.fmincon field to the real fmincon.
> 
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