Fix inflector to respect default locale.

The inflector was made aware of locales in 7db0b073fec6bc3e6f213b58c76e7f43fcc2ab97,
but it defaulted to :en. That should actually be our default
locale instead.

Fixes #10125
Merge pull request #10158 from steveklabnik/issue_10125

Fix inflector to respect default locale.
Add failing test case for #9654
Reverts rendering behavior when format is unknown

If a request has unknown format (eg. /foo.bar), the renderer
fallbacks to default format.

This patch reverts Rails 3.2 behavior after c2267db commit.

Fixes issue #9654.
Return nil for Mime::NullType#ref
Fixed typo
Merge pull request #10160 from choudhuryanupam/fix_typo_n_grammar

Fixed typo
Removed unused setup
Merge pull request #10162 from choudhuryanupam/fix_activesupport_test

Removed unused setup