fix for count when find has fields specified

lib/mongo/cursor.rb

@@ -66,7 +66,8 @@ module Mongo
     # database error.
     def count
       command = OrderedHash["count", @collection.name,
-                            "query", @query.selector]
+                            "query", @query.selector,
+                            "fields", @query.fields()]
       response = @db.db_command(command)
       return response['n'].to_i if response['ok'] == 1
       return 0 if response['errmsg'] == "ns missing"

test/test_cursor.rb

@@ -220,4 +220,14 @@ class CursorTest < Test::Unit::TestCase
     assert_equal(by_location,
                  @@db.db_command("cursorInfo" => 1)["byLocation_size"])
   end
+
+  def test_count_with_fields
+    @@coll.clear
+    @@coll.save("x" => 1)
+
+    @@coll.find({}, :fields => ["a"]).each do |doc|
+      fail "shouldn't have any results here"
+    end
+    assert_equal(0, @@coll.find({}, :fields => ["a"]).count())
+  end
 end