Added Ops.exists().

src/java/com/samskivert/depot/Ops.java

@@ -103,6 +103,14 @@ public class Ops
         return new Exists(target);
     }
 
+    /**
+     * Creates an EXISTS expression with the supplied select clause.
+     */
+    public static SQLExpression exists (SelectClause target)
+    {
+        return new Exists(target);
+    }
+
     /**
      * Adds the supplied expressions together.
      */