- default is now without polyhedral decomposition, since this produces
compacter files and VTK mananges this in most instances.
However, provide function object flag to reinstate the old behaviour.
- in many cases can just use lookupOrDefault("key", bool) instead of
lookupOrDefault<bool> or lookupOrDefault<Switch> since reading a
bool from an Istream uses the Switch(Istream&) anyhow
STYLE: relocated Switch string names into file-local scope