use the first 8 byte to be short.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@5766 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/matrix/MatrixConfiguration.java

@@ -113,7 +113,7 @@ public class MatrixConfiguration extends Project<MatrixConfiguration,MatrixRun>
         FilePath ws = node.getWorkspaceFor(getParent());
         if(ws==null)    return null;
         if(useShortWorkspaceName)
-            return ws.child(getCombination().digest());
+            return ws.child(getCombination().digest().substring(0,8));
         else
             return ws.child(getCombination().toString('/','/'));
     }