Rethink API wrt to operations not available on all platforms

[hvr]

Some time ago, based on the discussion in

http://thread.gmane.org/gmane.comp.lang.haskell.libraries/20865/focus=20936

@JohnLato prepared a patch at

JohnLato/packages-unix@a1d905c

that's risking to be forgotten.

[JohnLato]

Ah, I thought that had been merged already because it doesn't change semantics of anything. Although it's only a half-solution, in that it doesn't implement a custom exception type (which could change the behavior of existing programs).

[hvr]

@JohnLato Yeah, I forgot about it... sorry

btw, if you have time, it'd be great if you could turn that patch into a pull-request against this repository...

[JohnLato]

@hvr nearly done. Not sure what to do about System.Posix.DynamicLinker.Prim.packDL though. I guess I'd be in favor of warning if it's used when undefined, but maybe that behavior is just annoying?

[hvr]

@JohnLato thanks for updating the patch!

[hvr]

I've used this technique for the new operations added via

e14fbe2 and 98eced8

if this works out, we can convert the other existing functions with the next release (not sure yet if we'd need to major bump or just minor bump)