Added Funcs.countStar() because it's such a common SQL operation.

src/main/java/com/samskivert/depot/Funcs.java

@@ -53,6 +53,15 @@ public class Funcs
         return new Average<Number>(expr, true);
     }
 
+    /**
+     * Creates an aggregate expression that counts the number of rows that match the other clauses
+     * in this query.
+     */
+    public static FluentExp<Integer> countStar ()
+    {
+        return new Count(Exps.literal("*"));
+    }
+
     /**
      * Creates an aggregate expression that counts the number of rows from the supplied
      * expression. This would usually be used in a FieldOverride and supplied with a ColumnExp.

src/main/java/com/samskivert/depot/Query.java

@@ -373,7 +373,7 @@ public class Query<T extends PersistentRecord>
      */
     public int selectCount ()
     {
-        checkState(_groupBy == null, "Do you mean to select(Funcs.count(Exps.literal(\"*\")))?");
+        checkState(_groupBy == null, "Do you mean to select(Funcs.countStar())?");
         _fromOverride = new FromOverride(_pclass);
         return _repo.load(CountRecord.class, _cache, getClauseArray()).count;
     }