remove trailing whitespace from engines guide
fix the example code in the engines guide. closes #8583.
Merge pull request #9250 from senny/8583_fix_engines_documentation_example_code

fix example code in engines guide
test for regression from a712e08ebe21f6d8653a0e6602df2e0f5d40d9ca
reverted back our changes and added in the new define_method
Merge pull request #9206 from ranjaykrishna/use_define_method

Use define method instead of class_eval
Leave Session.create responsibility to the SessionStore

[Carlos Antonio da Silva + Santiago Pastorino]
Session = Rack::Session::Abstract::SessionHash

We had already ported all the Session methods to Rack, so there's no
need to duplicate everything here.

[Carlos Antonio da Silva + Santiago Pastorino]