utmpx on OpenBSD.

[Amar Takhar]

In 7d8b2d1 utmpx.h was always assumed to be available.  This is not true as 
OpenBSD does not have utmpx support.

There is no point in hoping for utmpx support in OpenBSD either I won't repeat 
the discussions here but there are plenty on the OpenBSD lists.

Can someone look at this please and bring it back?  The old way seems a little 
convoluted if there is a better way we should try it.

Thanks.


Amar.