Fix a bug such that, when parameters are asked to be randomised via useRandomInitFitPars, those parameters that are already fixed in the model, in addition to those that are fixed on import, are not subsequently freed.

git-svn-id: svn+ssh://phab.hepforge.org/source/laurasvn/trunk@546 30227d83-a2f9-49e9-9e98-657c83b2c86a