Should make object generation return values more consistent

[langfob]

Creating a Base or Wrap problem returns the problem object but doing a reserve selector run does not return the object. It returns a directory for UR_Forward and Gurobi, but a list containing a directory and a run time for Marxan. These are all correct, but it makes it more difficult to write uniform code that decodes and deals with the objects in a consistent way. This is coming up in writing example R code for these different objects in bdpg paper 1. It's not urgent to fix. Fixing it would no doubt also break some existing code that acts on the objects returned, so no rush to fix this.