This is no longer best-practice.

ref:
http://stackoverflow.com/questions/8344186/rails-3-1-on-apache-pagespeed-says-specify-cache-validator-when-using-asset-p/8348385#8348385

This reverts commit 8896b4fd.

Conflicts:

	activemodel/lib/active_model.rb
	activemodel/lib/active_model/serializable.rb
	activemodel/lib/active_model/serializer.rb
	activemodel/test/cases/serializer_test.rb

Test coverage isn't comprehensive enough to catch what this breaks. :(
This reverts commit 45dad592.

fix method redefined warnings in tests

fix warning in tests when using render_erb helper

Test helpers in erb using erb

ActiveRecord::Base.map method for direct select by single column

Log 'Filter chain halted as CALLBACKNAME rendered or redirected' every time a before callback halts.

`path_names` can only be used for affecting `new` and `edit`

Module#synchronize is deprecated with no replacement.  Please use `monitor` from ruby's standard library.

it clear which methods are synchronized.

the following code is deprecated:

Thread.new { Post.find(1) }.join

It should be changed to close the database connection at the end of
the thread:

Thread.new {
  Post.find(1)
  Post.connection.close
}.join

Only people who spawn threads in their application code need to worry
about this change.

pool.

This only existed to support methods like `set_table_name` in Active
Record, which are themselves being deprecated.