Fix SOVERSION to use only MAJOR to match ABI rules

[j-rivero]

The SOVERSION is currently coded to MAJOR.MINOR in Dart. If I'm not wrong, Dart follows semantic versioning so ABI is compatible in all minor versions of a major serie . If that is the case, I think that the current SOVERSION should be composed only by the major version.

[jslee02]

We intend to follow the semantic versioning, but I'm not sure if we strictly following it. I try to keep API compatibility over minors and patches in a major (with some accidental exceptions) but am not sure about ABI. Would this be the case?

[mxgrey]

The problem is that semantic versioning is a bit ambiguous when it comes to C++, because it's very possible to maintain API compatibility but break ABI compatibility.

DART's current policy is to maintain API compatibility between minor releases, and maintain ABI compatibility between patch releases, but we make no guarantee about ABI between minor releases.

I've opened an issue to propose that we maintain ABI compatibility between minor releases: #1026. However making that feasible would require a major overhaul to how DART is implemented, and it's not clear to me when or if we'd have time for that.

[mxgrey]

But while the current policy exists, we do need both major and minor versions as part of the SOVERSION.

[j-rivero]

I was not aware of the lack of clarity in semantic versioning respect to the ABI. Thanks for explanation, I will rename the dart packages in Debian according to the policy (grep for package-name-doesnt-match-sonames in the Jenkins build log)

It would be good if we can keep packages with the same name in both upstream Debian and the PPA https://launchpad.net/~dartsim/+archive/ubuntu/ppa/+packages .