CommitsSinceTag is incorrect

[SimonCropp]

so CommitsSinceTag is populated by this https://github.com/Particular/GitVersion/blob/master/GitVersionCore/GitFlow/BranchFinders/OptionallyTaggedBranchVersionFinderBase.cs#L15 which is actually the "commits since branch" not "Commits Since Tag"

[JakeGinnivan]

Commit counting has completely changed.

It now counts from the source of the version. With the exception of NextVersion in the config, it falls back to the next best source for commit counting