Fix response not changing with parallel requests

In this order the @env would not be changed by the "on complete"
callbacks, meaning that the response would not change after parallel
requests finish (e.g. JSON would not be parsed).

This would work

  def on_complete(env)
    env[:body].upcase!
  end

But this wouldn't

  def on_complete(env)
    env[:body] = env[:body].upcase
  end
Merge pull request #378 from janko-m/fix-parallel-parsing

Fix response not changing with parallel requests
Fix ActiveSupport::SafeBuffer#gsub bug 

.. in NestedParamsEncoder
Merge pull request #381 from alagu/master

Fix ActiveSupport::SafeBuffer#gsub bug
Lock rest-client to ~> 1.6.0 on Ruby 1.8.7
Update README with env usage in stubs
Don't require SimpleCov on Ruby 1.8
Merge pull request #388 from Nitrodist/update-readme-with-env-usage

Update README with env usage in stubs
Remove timeout from request autoloads, since it was removed in 43343e971f4bb9366daa1188272389166396a5c0
Merge pull request #407 from loopj/remove-timeout-autoload

Remove request/timeout from autoloads, since it has been removed
Fix passing ActiveSupport::SafeBuffer to param encoders

Simply re-use `Faraday::Utils.escape/unescape` instead of reimplementing
them for each encoder.