moved sql related code to its own engine area

Conflicts:

	lib/arel/engine.rb
	lib/arel/extensions/object.rb
	lib/arel/predicates.rb
	lib/arel/primitives/attribute.rb
	lib/arel/primitives/expression.rb
	lib/arel/primitives/value.rb
	lib/arel/relations/operations/join.rb
	lib/arel/relations/relation.rb
	lib/arel/relations/utilities/externalization.rb
	lib/arel/relations/utilities/nil.rb
	lib/arel/relations/writes/delete.rb
	lib/arel/relations/writes/insert.rb
	lib/arel/relations/writes/update.rb
	spec/arel/unit/relations/skip_spec.rb
	spec/arel/unit/relations/take_spec.rb
	spec/spec_helper.rb

1 files changed, 1 insertions, 1 deletions

diff --git a/doc/TODO b/doc/TODO
index ad12640881..8a8dcf5380 100644
--- a/doc/TODO
+++ b/doc/TODO
@@ -1,5 +1,5 @@
 todo:
-
+- expressions should be class-based, and joins too, anything _sql should be renamed
 - refactor adapter pattern
 - implement in memory adapter
 - implement mnesia adapter