now able to set file_system for include tag through registers

lib/liquid/tags/include.rb

@@ -24,7 +24,8 @@ module Liquid
     end
   
     def render(context)      
-      source  = Liquid::Template.file_system.read_template_file(context[@template_name])      
+      file_system = context.registers[:file_system] || Liquid::Template.file_system
+      source  = file_system.read_template_file(context[@template_name])      
       partial = Liquid::Template.parse(source)      
       
       variable = context[@variable_name || @template_name[1..-2]]

test/include_tag_test.rb

@@ -24,12 +24,21 @@ class TestFileSystem
     when "recursively_nested_template"
       "-{% include 'recursively_nested_template' %}"
 
+    when "pick_a_source"
+      "from TestFileSystem"
+      
     else
       template_path
     end
   end
 end
 
+class OtherFileSystem
+  def read_template_file(template_path)
+    'from OtherFileSystem'
+  end
+end
+
 class IncludeTagTest < Test::Unit::TestCase
   include Liquid
   
@@ -37,6 +46,11 @@ class IncludeTagTest < Test::Unit::TestCase
     Liquid::Template.file_system = TestFileSystem.new    
   end
   
+  def test_include_tag_looks_for_file_system_in_registers_first
+    assert_equal 'from OtherFileSystem',
+                 Template.parse("{% include 'pick_a_source' %}").render({}, :registers => {:file_system => OtherFileSystem.new})
+  end
+  
 
   def test_include_tag_with    
     assert_equal "Product: Draft 151cm ",