make pool_prepared_statements always prepare statement in connection

spec/database_spec.cr

@@ -140,6 +140,18 @@ describe DB::Database do
         db.build("the query").should be_a(DB::PoolUnpreparedStatement)
       end
     end
+
+    it "should be overrided by dsl" do
+      with_dummy "dummy://localhost:1027?prepared_statements=true" do |db|
+        stmt = db.unprepared.query("the query").statement.as(DummyDriver::DummyStatement)
+        stmt.prepared?.should be_false
+      end
+
+      with_dummy "dummy://localhost:1027?prepared_statements=false" do |db|
+        stmt = db.prepared.query("the query").statement.as(DummyDriver::DummyStatement)
+        stmt.prepared?.should be_true
+      end
+    end
   end
 
   describe "unprepared statements in pool" do

src/db/pool_prepared_statement.cr

@@ -34,7 +34,7 @@ module DB
       clean_connections
       conn, existing = @db.checkout_some(@connections)
       @connections << WeakRef.new(conn) unless existing
-      conn.build(@query)
+      conn.prepared.build(@query)
     end
 
     private def clean_connections