This causes Idris to not emit messages about "Type checking ...." while
in quiet mode, which improves the portability of tests to Windows (due
to the slash facing the other way there). It also makes tests a bit more
robust with regards to their source files changing names.
They can be imported from the modules Data.Fin, Data.Vect, and Data.So
respectively.
The general thinking here is that not every program is going to need
these, and they are often used especially by newcomers in place of
something more appropriate. Also, all of them are useful for teaching,
which means it is instructive for tutorials to introduce them and have
people implement them themselves.
