Added PoissonFormulation.
Added support for x(), y() and z() component methods to SimpleSolutionFunction (the Function subclass that is used by Function::solution()).

This means that you can now have a vector trial variable u and do:

FunctionPtr u_soln = Function::solution(u, soln);
FunctionPtr u_x = u_soln->x();

etc.
Commented out some console output.
Added a test against the traceTerm stuff (specifically was concerned about fluxes).  It passes.
Added access to Aztec iteration count and nominally condest.  However Aztec just returns -1 for condest, despite an estimate having been printed.
Revised GMGTests to use the new PoissonFormulation.