Revert "Raise FilterNotFound on use of non-existent filter"

This reverts commit 01c25a11a3.

Conflicts:

	test/context_test.rb

lib/liquid/context.rb

@@ -57,7 +57,7 @@ module Liquid
       if strainer.respond_to?(method)
         strainer.__send__(method, *args)
       else
-        raise FilterNotFound, "Filter '#{method}' not found"
+        args.first
       end
     end
 

test/context_test.rb

@@ -155,9 +155,7 @@ class ContextTest < Test::Unit::TestCase
     assert_equal 'hi? hi!', context.invoke(:hi, 'hi?')
 
     context = Context.new
-    assert_raises(FilterNotFound) {
-      context.invoke(:hi, 'hi?')
-    }
+    assert_equal 'hi?', context.invoke(:hi, 'hi?')
 
     context.add_filters(filter)
     assert_equal 'hi? hi!', context.invoke(:hi, 'hi?')

test/security_test.rb

@@ -11,14 +11,14 @@ class SecurityTest < Test::Unit::TestCase
 
   def test_no_instance_eval
     text = %( {{ '1+1' | instance_eval }} )
-    expected = %! Liquid error: Error - filter 'instance_eval' in ''1+1' | instance_eval' could not be found. !
+    expected = %| 1+1 |
         
     assert_equal expected, Template.parse(text).render(@assigns)
   end
   
   def test_no_existing_instance_eval
     text = %( {{ '1+1' | __instance_eval__ }} )
-    expected = %! Liquid error: Error - filter '__instance_eval__' in ''1+1' | __instance_eval__' could not be found. !
+    expected = %| 1+1 |
         
     assert_equal expected, Template.parse(text).render(@assigns)
   end
@@ -26,7 +26,7 @@ class SecurityTest < Test::Unit::TestCase
 
   def test_no_instance_eval_after_mixing_in_new_filter
     text = %( {{ '1+1' | instance_eval }} )
-    expected = %! Liquid error: Error - filter 'instance_eval' in ''1+1' | instance_eval' could not be found. !
+    expected = %| 1+1 |
   
     assert_equal expected, Template.parse(text).render(@assigns)
   end
@@ -34,7 +34,7 @@ class SecurityTest < Test::Unit::TestCase
 
   def test_no_instance_eval_later_in_chain
     text = %( {{ '1+1' | add_one | instance_eval }} )
-    expected = %! Liquid error: Error - filter 'instance_eval' in ''1+1' | add_one | instance_eval' could not be found. !
+    expected = %| 1+1 + 1 |
   
     assert_equal expected, Template.parse(text).render(@assigns, :filters => SecurityFilter)
   end