add a magic 'there's a new version to download' string to b2d-cli version

[SvenDowideit]

ala docker.

and it would be good to indicate the version of docker they're running. Eventually, it would be good to tie the version numbers together

[SvenDowideit]

boot2docker/boot2docker#285

[riobard]

There are three versions we need to show: the boot2docker ISO version, the boot2docker-cli version, and the docker version. For the latter two it's relatively easy to get the version strings locally and compare with the GitHub release tags. I'm not sure how to figure the version of a local ISO image. Any suggestions?

[gmlewis]

Maybe we can get @SvenDowideit to add either an MD5 or SHA1 hash to this service:
https://api.github.com/repos/boot2docker/boot2docker/releases
and then we could simply reverse-lookup the hash of the current local ISO to report the version number.

[tianon]

If we can get a very simple ISO file format reader going, there is a "version" file inside that can be used. 7z can get at it trivially, but I think a dep on 7z just to determine the version number of our local ISO would be absurd. :)

[riobard]

@tianon Yeah, that's a bit overkill :)

I like @gmlewis's proposal. The hash of ISO images can be used for integrity check after downloading too, so we get double benefits :) @SvenDowideit will you be able to add a hash to the GitHub releases?

[riobard]

@SvenDowideit is there any plan to add hashes of the ISO files?

[SvenDowideit]

yes, a plan exists.

[tianon]

Sorry, this repository is long-since deprecated in favor of Docker Toolbox (whose usage is now also discouraged in favor of Docker for Windows and Docker for Mac).