Noting that and why gmxdump -s -sys is broken

Not worth fixing. You could pass a boolean from gmxdump
into the set_posres_params to avoid executing the
problematic line, but that would hit a lot of
other code paths that also call gmx_mtop_to_t_topology.

Refs #635

Change-Id: I308e59287dc578b95ea67c313867df3e75047fa4
Merge "Noting that and why gmxdump -s -sys is broken" into release-4-5-patches