Improve the testing guide [ci skip]

Improve the "Testing Rails Applications" guide adding a section for
testing helpers and a little note about associations with ActiveRecord
and YAML fixtures.

Also add a link to Fixture Builder ; yet another replacement for
fixtures such as Machinist or FactoryGirl.
Added SanitizeHelper to rails guide docs [ci skip]

Added SanitizeHelper to rails guide docs [ci skip]

Added SanitizeHelper to rails guide docs update [ci skip]
document `assert_not_XYZ` in place of `refute_XYZ`.
Removed redundant asserts for assigns attribute operation
Rescue invalid ip address exceptions on assign.

In order that set attribute should not be bang method
Typo Fix[ci skip]
Fixing multi-word automatic inverse detection.

Currently, ActiveRecord models with multiple words cannot have their
inverse associations detected automatically.
Adding LESS to rake notes
fix build error caused by #11900.
Use binary mode to write uploaded files [ci skip] See: http://stackoverflow.com/a/4988984/129798 for an explanation for why this is required for Ruby 1.9.