Removed documentation for the removed rollback! method on transactions and mention ActiveRecord::Rollback [cody]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8240 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/lib/active_record/transactions.rb

@@ -30,17 +30,6 @@ module ActiveRecord
     # Exceptions will force a ROLLBACK that returns the database to the state before the transaction was begun. Be aware, though,
     # that the objects by default will _not_ have their instance data returned to their pre-transactional state.
     #
-    # == Rolling back a transaction manually
-    #
-    # Instead of relying on exceptions to rollback your transactions, you can also do so manually from within the scope
-    # of the transaction by accepting a yield parameter and calling rollback! on it. Example:
-    #
-    #   transaction do |transaction|
-    #     david.withdrawal(100)
-    #     mary.deposit(100)
-    #     transaction.rollback! # rolls back the transaction that was otherwise going to be successful
-    #   end
-    #
     # == Different ActiveRecord classes in a single transaction
     #
     # Though the transaction class method is called on some ActiveRecord class,
@@ -80,7 +69,8 @@ module ActiveRecord
     # == Exception handling
     #
     # Also have in mind that exceptions thrown within a transaction block will be propagated (after triggering the ROLLBACK), so you
-    # should be ready to catch those in your application code.
+    # should be ready to catch those in your application code. One exception is the ActiveRecord::Rollback exception, which will
+    # trigger a ROLLBACK when raised, but not be re-raised by the transaction block.
     module ClassMethods
       def transaction(&block)
         previous_handler = trap('TERM') { raise TransactionError, "Transaction aborted" }