Revert "Switched to newer rdoc and gem package tasks (and their requires)."

This is a manual revert of commit 79aa54d, since the commit itself touches
in addition some version numbers.

API generation before Rails 3 uses the Jamis template, which requires an
old version of RDoc. To generate the API you need Rake 0.8.x or 0.9.x,
and the RDoc distributed with 1.8.7 (version 1.0.1).
stop calling to_sym when building arel nodes [CVE-2013-1854]
fix incorrect ^$ usage leading to XSS in sanitize_css [CVE-2013-1855]

Conflicts:
	actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb
fix protocol checking in sanitization [CVE-2013-1857]

Conflicts:
	actionpack/lib/action_controller/vendor/html-scanner/html/sanitizer.rb
	actionpack/test/controller/html-scanner/sanitizer_test.rb
Revert "Revert "Switched to newer rdoc and gem package tasks (and their requires).""

I can't build the gems without reverting this commit.

This reverts commit dad31097a21e0f2249820a756eafe792076ced9c.
bumping to 2.3.18
Merge remote-tracking branch 'rails/2-3-stable' into staging