Wcondprod shut

This PR fixes a bug in the WellsManager code, where the 'C variable' `well_index` is not updated in the case of a shut well. In addition there is some minor improvements & bug fixes for SHUT wells.

Should be merged after: https://github.com/OPM/opm-parser/pull/326
Why the `15*` rather than "just" an early record termination?