Address problems with constraints reported in #1060 and #1064
Merge pull request #1107 from nden/constraints_issues

Address problems with constraints reported in #1060 and #1064

There's still a minor issue with constraints which is that after fitting the constraint attributes on the parameter objects are reset to the default values. But the model.constraints object has the correct values. I am going to merge this so it can be used and will open a different issue for this last problem I am aware of. It doesn't affect fitting but can be misleading.