Fix broken rendering of variables which are equal to false (closes #345)

lib/liquid/context.rb

@@ -194,7 +194,8 @@ module Liquid
 
         if scope.nil?
           @environments.each do |e|
-            if variable = lookup_and_evaluate(e, key)
+            variable = lookup_and_evaluate(e, key)
+            unless variable.nil?
               scope = e
               break
             end

test/integration/context_test.rb

@@ -20,5 +20,4 @@ class ContextTest < Test::Unit::TestCase
     assert_equal 'Global test', Template.parse("{{'test' | notice }}").render!
     assert_equal 'Local test', Template.parse("{{'test' | notice }}").render!({}, :filters => [local])
   end
-
 end

test/integration/variable_test.rb

@@ -25,6 +25,10 @@ class VariableTest < Test::Unit::TestCase
     assert_equal 'worked', template.render!('test' => {'test' => 'worked'})
   end
 
+  def test_false_renders_as_false
+    assert_equal 'false', Template.parse("{{ foo }}").render!('foo' => false)
+  end
+
   def test_preset_assigns
     template = Template.parse(%|{{ test }}|)
     template.assigns['test'] = 'worked'