- exists() = forward to OSspecific exists(...)
- isDir() = forward to OSspecific dir(...)
- isFile() = forward to OSspecific file(...)
- IOobjectComponents() - split into instance, local, name following rules
set out for IOobject.
- added IOobject(path, registry, ...) constructor that uses
fileName::IOobjectComponents(). This hides the complexity we otherwise need.
- if mandatory is true, findEtcFile() will abort with a message (via cerr).
This allows a non-existent file to be caught at the lowest level and avoid
error handling in IFstream, which might not be initialized at that stage.
