Context: A relibc fork check via cargo compare exposed that the fork
labeled 0.6.0 (matching a 2020-12-23 upstream tag) was on a
completely different codebase from upstream master. The fork was
imported as a snapshot. The verify-fork-versions.sh tool allowed
this because 'snapshot' mode skipped byte-for-byte content comparison.
Changes:
1. Remove 'snapshot = skip content check' behavior. All Cat 2 forks must
pass actual content comparison against their claimed upstream tag.
2. Add base to local/fork-upstream-map.toml so it's checked too (was missing).
Effect: Future 'fake version label' divergences (Cargo.toml says
version X but source content does not match upstream X) will be
caught by the preflight check instead of slipping through build.
vasilito
7d134eef37