More flexible :fields option, supporting {}

This allows exact definition of the fields you want included in the query results. For example :fields => {:name => 1, :people => 0} will include the name key but exclude the people key.

lib/mongo/cursor.rb

@@ -282,6 +282,8 @@ module Mongo
           returning({}) do |hash|
             fields.each { |field| hash[field] = 1 }
           end
+        when Hash
+          return fields
       end
     end
 

test/unit/cursor_test.rb

@@ -30,6 +30,13 @@ class CursorTest < Test::Unit::TestCase
       assert @cursor.fields == {:name => 1, :date => 1}
     end
 
+    should "set mix fields 0 and 1" do
+      assert_nil @cursor.fields
+
+      @cursor = Cursor.new(@collection, :fields => {:name => 1, :date => 0})
+      assert @cursor.fields == {:name => 1, :date => 0}
+    end
+
     should "set limit" do
       assert_equal 0, @cursor.limit