Conditionally drop the usage of Errno in favor of File::Error

[bcardiff]

No description provided.

[Sija]

Some TODO: remove after ... would be good to have.

[bcardiff]

For me all compare_versions are subject to be removed eventually. They will go when the mentioned version is wanted to be dropped. That might not depend on the version of the main lib or app. So it's hard to say, to be removed after x.y.z.

[ysbaddaden]

Let's not bother with conditionals: master will only compile against crystal master, which is fine IMO.

[j8r]

If one needs a latest shards and an older crystal compiler, which is not that common, (s)he can use a statically linked shards, from the official archives or compile it.

[bcardiff]

@waj feedback addressed.

I forgot to send/mention that to test this on 0.34.0 we need an update & release of minitest ysbaddaden/minitest.cr#38

[RX14]

Shards doesn't have to bootsrap itself from the previous crystal version, there's no need for it to compile on both.

Shards has always been released in lockstep with Crystal and this has been fine in the past.

[bcardiff]

Shards CI runs on latest, no master. That and the possibility of using a new shards version leads to the need for shards to compile on the latest released Crystal and not just nightly.

I have restarted the osx failure. OSX travis build should go away and build on other provider.

This PR can be merged and later we handle the story for specs on Crystal master.

[bcardiff]

Rebased on master. No further changes done.

I will refactor the logging on another PR.