Check for implicit solvent + Verlet scheme

Fixed #1570

Change-Id: I8734c2dc99d3bc3e0a79ae043d86854446f3b495
Fixed DD state collection issue

Collecting the cg distribution state to the master (for output
of replica exchange) could go wrong when the DD was out of sync.
This code path was probably never executed.

Change-Id: I14b41c15ddc827a46f7c6448fb7bd90414f8e210