Rename on-connection-* into tunnel-* and simplify related code.

[vspinu]

The names on-connection-buffer and on-connection-process are pretty confusing. They provide tunneling and are unlikely to be used for anything else, so let's name them as such.

Some simplification/clarification of the code and documentation were made here and there and nrepl-connection-endpoint returns the process instead of the process' buffer-name. I think it's good to work with first principles whenever possible.

I have also increased the process-wait-for-output timout to .05. On some machines, keeping it very low makes Emacs pinging continuously up to the point that C-g doesn't work anymore. This happens mostly on windows but people reported this on linux as well. It doesn't harm to have it higher in this particular place. It's far from noticeable and the process returns faster on any input anyways. Better safe than sorry.

[bbatsov]

See the discussion we had with @hugoduncan regarding those names #489. There're not optimal I guess, but I don't think your suggestion is an improvement.

[vspinu]

The proposed naming is good because nrepl-tunnel-buffer and nrepl-tunnel-process are helpers for nrepl-connection-ssh-tunnel and these names make it very clear.

The naming is not perfect because if there will be some other mechanism which would use a helper process which is not a tunnel, it will require a new variable. But how likely is that? If this ever happens you can rename this vars back to on-connection-xxx or a better name as you will have yet another example of a helper process.

I actually think that the configurable variable nrepl-connection-endpoint is not necessary at this stage. It's simply confusing because nrepl-connection-ssh-tunnel does all the job anyways.

[vspinu]

I am taking another stab on this. This time I completely removed the customization machinery around ssh tunneling and replaced it with one function nrepl-connection-endpoint which does all the job.

I think this simplicity really wins over the alternative of the unlikely-to-be-used customization and confusing names.

[bbatsov]

@Vitoshka That's fine by me if it's fine by @hugoduncan. I can't think of other realistic use cases for this so the change makes sense to me.

[hugoduncan]

As long as cider-jack-in in a tramp buffer still works, fine with me.

[bbatsov]

@Vitoshka You'll have to rebase this.

[vspinu]

@Vitoshka That's fine by me if it's fine by @hugoduncan. I can't think of other
realistic use cases for this so the change makes sense to me.

If there are other general use cases then we should code them into
nrepl-connection-endpoint.

If some user would want something very specific then he can always use
advice or completely rewrite nrepl-connection-endpoint for his use. It
just doesn't feel right to have this as a custom variable.

[vspinu]

Rebased on #792 to avoid any further complications.