Use preferred phase to compute wellbore mix for dead wells
The wellmore mix is set to preferred phase for dead wells, where the
total volumetric rates are zero. This sets the phase of the flow out of
perforations in dead wells and thus avoids zero volumerats for injecting
preforations in dead wells.
Merge remote-tracking branch 'totto82/fix_welleq' into fix_welleq
Remove unnecessary argument, and minor formatting corrections.
Merge pull request #117 from atgeirr/fix_welleq

Fix NaNs for well equations.