Availability of various calls

[Chris Ridd <chris@imc.exec.nhs.uk>]

I'm looking a little at how to make the mintlibs more independant of the
Mint version, so it will work better on other OSes (eg MagiC) and extensions
(eg MetaDOS).

So, I was wondering: are the Directory scanning calls Dopendir, Dreaddir,
Drewinddir, and Dclosedir always available for all drives, or are they just
available on a per-drive basis?

Would they also be available on all media used in removeable drives?

Looking ahead somewhat, would it be sensible to assume that if a call like
Psignal() is implemented, Pkill/Psigaction/etc are also implemented?

Chris