3894: gem version numbers reflect latest commit in the subdirectory
where the gem content comes from.

Even if there are more recent commits elsewhere in the source tree,
those changes won't be reflected in the package so there's no need to
increment the package version.

In addition to avoiding the proliferation of packages with no changes
other than the version number, this makes it possible to change an
SDK, predict the gem version that the CI server will build, refer to
that version in a Gemfile elsewhere in the source tree, and push both
changes at once -- without time travel.
3894: Fix up runtime dependency specs to make bundle comfortable.
3894: Merge branch 'master' into 3894-gem-version
3894: Use git log --first-parent to get nearest commit/merge on
current branch to label package version, rather than nearest
commit. This ensures the package version number increases when an
older commit is merged after a newer commit.
3894: Remove outdated README.
3894: Merge branch 'master' into 3894-gem-version
3894: Set arvados version in Gemfile.lock to one that exists.
Merge branch '3894-gem-version' refs #3894