branch-2.1.0-alpha doesn't build due to the following. Per YARN-1 I updated the mvn version to be 2.1.0-SNAPSHOT, before I hit this issue it didn't compile due to the bogus version.
hadoop-branch-2.1.0-alpha $ mvn compile
[INFO] Scanning for projects...
[ERROR] The build could not read 1 project -> [Help 1]
[ERROR] The project org.apache.hadoop:hadoop-yarn-project:2.1.0-SNAPSHOT (/home/eli/src/hadoop-branch-2.1.0-alpha/hadoop-yarn-project/pom.xml) has 1 error
[ERROR] 'dependencies.dependency.version' for org.hsqldb:hsqldb:jar is missing. @ line 160, column 17