The version information generated during the build of common when running from git has revision and branch Unknown. I believe this started after the unsplit:
@HadoopVersionAnnotation(version="0.22.0-SNAPSHOT", revision="Unknown", branch="Unknown",
user="tgraves", date="Tue Jun 14 13:39:10 UTC 2011", url="file:///home/tgraves/git/hadoop-common/common",
The ./src/saveVersion.sh script which generates the package-info.java file with the version info looks for the presence of .git directory and that is now a level up instead of in the common directory.