Disallow calls to IDistribution1D::probabilityDensity if width is zero
In child classes of Distribution1D, the probabilityDensity has to handle the special case of width zero. It currently does so by returning 0 if x==mean, otherwise 0. This attempt to implement a delta distribution is flawed. Normalization is wrong.
- ASSERT(width>0). No need then to implement return values for the case mean=0.
- Prevent probabilityDensity from being called if width=0.