i.e. remove the defaultSet() method and its friends. this is required
to be able to specify defaults in DATA items like grid properties or
saturation tables. e.g.
SGL
10*0.1 10* 10*0.2 /
would not be possible without this. If no meaningful default for an
item is defined, float and double items get NaN, int items get -1 and
string ones get an empty string. The hope is that if these values get
used in the simulation, they will make the result obviously
incorrect. (Whether a data point of an item was defaulted can be
queried using item->defaultApplied(index).)