Updating documentation for Console. Now mentioniing sandbox and including a link to the irb section in the online Pickaxe.

Conflicts:
	activesupport/lib/active_support/core_ext/hash/conversions.rb

Temporarily add submodules to the Rails repo for Arel and Rack::Mount. These submodules will be removed once we add proper Gemfile following to bundler

[#3259 state:resolved]
Signed-off-by: NEloy Duran <eloy.de.enige@gmail.com>

Revert "Split arel_table into method to get a relation and another to memoize the default relation."

This reverts commit bd517908.

Ruby 1.9.2: disallow explicit coercion via method_missing. Only give friendly nil errors for Array and Active Record methods.