AS guide: removes the placeholder for extensions to Benchmark because benchmark.rb just reimplements an existing method

AS guide: removes the placeholder for extensions to Exception because exception.rb seems to provide stuff for internal use

AS guide: removes CGI placeholder section,  CGI.escape_skipping_slashes seems something for internal use

AS guide: reflects the guide finally covers only core extensions (is gonna be one of the biggest ones just with that)

Caching guide: documents that page/action caching run in an after_filter, and this spurious cache entries are avoided just by halting the request

Add a :limit option to specify the maximum number of records that can be processed by accepts_nested_attributes_for

Store entire options hash in the class var rather than just the reject_if proc for the nested attributes

Signed-off-by: NCarl Lerche <carllerche@mac.com>

Ruby 1.9: Fix ActiveResource::ConnectionError#to_s when @response does not respond to #code or #message
Signed-off-by: NCarl Lerche <carllerche@mac.com>

Conflicts:

	activerecord/lib/active_record/nested_attributes.rb