modqueue: optimize sql queries.

* Include appeals and flags.
* Avoid an existence query for pools.
* Avoid a query checking if the user has previously approved the post.
  This is a rare condition and it will be prevented anyway if the user
  tries to reapprove the post.

test/unit/post_approval_test.rb

@@ -22,10 +22,6 @@ class PostApprovalTest < ActiveSupport::TestCase
       CurrentUser.ip_addr = nil
     end
 
-    should "allow approval" do
-      assert_equal(false, @post.approved_by?(@approver))
-    end
-
     context "That is approved" do
       should "create a postapproval record" do
         assert_difference("PostApproval.count") do