Builds should fail early with snapshot mismatches

In a given release, all snapshot dependencies should have the same patch level: .0-SNAPSHOT when we’re leading up to GA, .1-SNAPSHOT leading up to SR1, etc. We could easily check builds for this and fail them early — this would catch mis-matches in patches (which catch a lot of developers out), and help reduce the risk of merging patches with obsolete versions after a release bump.