CustomProperties, IncidenceBase, Incidence - Add warning that the operator= and operator== are not polymorphic.

Event, FreeBusy, Journal, Todo

• Call operator==() of the super class instead of using static casts.

ComparisonVisitor

• New concrete IncidenceBase::Visitor for comparing instances of the IncidenceBase subclasses Event, FreeBusy, Journal and Todo

svn path=/trunk/KDE/kdepimlibs/; revision=949600