doc fixes

Removed Unused Variable. 

Fix failing asset debug test under 1.8

error.  Strings tagged as binary will be stored in sqlite3 as blobs.  It
is an error to insert binary data to a string column, so an error is
emitted in the log file.  People are highly encouraged to track down the
source of the binary strings and make sure that the encoding is set
correctly before inserting to the database.

Documentation changes: Assets Pipeline guide and Railties changelog

Removing redundant stringify_keys in Sprockets helpers

Don't require a specific value for the ?debug flag

Previously, only "1" and "true" were accepted. This change makes
any value, or no value at all, have the same effect.

Fix broken test test_copying_migrations(RailtiesTest::EngineTest):
NoMethodError: undefined method `log_level' for #<Rails::Engine::Configuration:0xb87a98c>

Make Sprockets::Helpers::RailsHelper#debug_assets? more readable

Refactor asset debugging tests

Moved strict validation changelog entry to right place

fix destructive stringify_keys for label_tag

Implemented strict validation concept

Also:

- Refactor AssetDebuggingTest.
- Use the %r regexp syntax. That way we don't need to escape the /'s.

do not compute table names for abstract classes

Add back autoload :Table

Refactoring javascript_include_tag and stylesheet_link_tag Sprockets helpers