Resolve #430 (Add normalisation flag to constrained prior)

This MR resolves issue #430 (closed) to properly normalize ConstrainedPriorDict.prob() when sampling the prior. This MR allows for users to input a normalisation flag when creating an instance of a Constraint prior and when calling ConstrainedPriorDict.prob() if there are normalisation constants given will return the normalisation*prob and otherwise use the ratio of total samples to kept samples as this normalisation constant. Pass normalisation=1 when creating a Constraint Prior for behaviour before this MR.

bilby/core/sampler/pymultinest.py

@@ -81,6 +81,10 @@ class Pymultinest(NestedSampler):
                 .format(self.kwargs['outputfiles_basename']))
         check_directory_exists_and_if_not_mkdir(
             self.kwargs['outputfiles_basename'])
+
+        # for PyMultiNest >=2.9 the n_params kwarg cannot be None
+        if self.kwargs["n_params"] is None:
+            self.kwargs["n_params"] = self.ndim
         NestedSampler._verify_kwargs_against_default_kwargs(self)
 
     def _apply_multinest_boundaries(self):