Avoid energy drift with verlet-buffer-tolerance

Added a warning with weak coupling and SD when tau_t and
verlet-buffer-tolerance as so large that the temperature might
be off by more than 0.2%.
Turned off nstlist tuning in mdrun with nstlist=1.
Also fixed Andersen checks in mdrun that were useless, since they
were done before temperature coupling groups were set.

Change-Id: I41bd316449c9e03e21d33dd82ebeab034d019fc6