[Resolver] Show a helpful error message if the old resolver incorrectly activated a   pre-release version that now leads to a version conflict
Merge pull request #2806 from CocoaPods/seg-old-lockfile-prerelease

[Resolver] Show a helpful error message if the old resolver incorrectly activated a   pre-release version that now leads to a version conflict
[pod spec create] Handle repos without commits

Fixes #2803