[HG DOLFIN] Update Poisson demo.

[dolfin-dDist1jlEr4dnm+ (DOLFIN)]

One or more new changesets pushed to the primary dolfin repository.
A short summary of the last three changesets is included below.

changeset: 7468:e8a51029713a
tag: tip
user: "Garth N. Wells <gnw20-KWPb1pKIrIJaa/***@public.gmane.org>"
date: Tue Nov 17 00:32:41 2009 +0000
files: demo/pde/poisson/cpp/main.cpp dolfin/function/Expression.cpp dolfin/function/Expression.h
description:
Update Poisson demo.


changeset: 7467:0197ae520596
user: "Garth N. Wells <gnw20-KWPb1pKIrIJaa/***@public.gmane.org>"
date: Mon Nov 16 23:46:04 2009 +0000
files: dolfin/function/Expression.cpp dolfin/function/Expression.h site-packages/dolfin/compile_expressions.py
description:
Remove old Expreesion::eval(...) function.


changeset: 7466:2cb787358636
user: "Garth N. Wells <gnw20-KWPb1pKIrIJaa/***@public.gmane.org>"
date: Mon Nov 16 23:25:30 2009 +0000
files: site-packages/dolfin/expression.py test/unit/function/python/test.py
description:
Comment out some Python function unit tests.

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