Include existing prologix-GPIB-ethernet code for ibcon and friends

[varenius]

As per a discussion in #53, local OSO-files which enable FS communication with prologix GPIB-ethernet units (in addition to direct GPIB units), was discussed. This code has been in use at OSO for many years, and works very well.
@wehimwich suggested that

We can look into getting that merged into the FS if you all would like. In the meantime, we could at least include the changes to boss/rdtib.f; they look entirely backward compatible. That way you won't have to re-update it when there is a new FS release. Life is easier if the working directory is clean. :)

In the meantime. I would encourage moving Mikael's version of ibcon to /usr2st, for the same reason. The only revisions necessary for that should be to change the .. references in the Makefile to ../../fs, the same change to include file references in the code, and to add it to /usr/st/Makefile. OTOH, if the ibcon changes are backward compatible, maybe they could be merged in first. It make be a little while until there is a chance though since we have to be really sure they are backward compatible. We could also put it on another branch initially.

Originally posted by @wehimwich in #53 (comment)

As far as I know, the prologix-modifications are all entirely backwards compatible with existing code. It would indeed be nice to not have to modify files with local copies for FS installs/upgrades. But I don't know all the details. As Mikael L is the author of these features, I will ask him to comment here, and we can then discuss the steps to include the code in the standard FS.

[varenius]

Mikael L is currently busy with other things, but sent me the documentation for our OSO-IBCON which I attach here
in PDF format.

I note the sentence "This version is available for other VLBI stations which want to use network-based communication and could also be included in a future release of the FS, since it won’t require any modifications for VLBI stations which continue to communicate via a GPIB-card.".

So, the way I understand it, it should be backwards compatible. I will ask Mikael L to do a pull-request with his code once he has time (likely in august).

[wehimwich]

A pull request would be greatly appreciated. The time frame is not a problem since I am pretty busy until at least then anyway.

[varenius]

Pull request has now been made by Mikael Lerner in #132