Make fast realtime decomposition use the proper nobs

See https://github.com/DynareTeam/dynare/pull/1563#issuecomment-357180435

This means that the option should be implemented in preprocessor to work as: realtime_shock_decomposition(fast_realtime = INTEGER)

added preprocessor label

added bug label

changed milestone to %4.6

The preprocessor already supports the argument fast_realtime = INTEGER to realtime_shock_decomposition (done in preprocessor@b94ff64c). @JohannesPfeifer does this issue now only concern the backend?

To me it seems the issue has been fixed in dde1acd1. The backend seems fine. Closing the issue.

closed