Using latest AR-JDBC for JRuby

The dependency was introduced in this commit:

002713c6

which has been released a long time ago

This reverts commit 9c18b6a8.

This reverts commit fba97c96.

Move the Journey code underneath the ActionDispatch namespace so
that we don't pollute the global namespace with names that may
be used for models.

Fixes rails/journey#49.

Summary of the changes:
 * Add thread_safe gem.
 * Use thread safe cache for digestor caching.
 * Replace manual synchronization with ThreadSafe::Cache in Relation::Delegation.
 * Replace @attribute_method_matchers_cache Hash with ThreadSafe::Cache.
 * Use TS::Cache to avoid the synchronisation overhead on listener retrieval.
 * Replace synchronisation with TS::Cache usage.
 * Use a preallocated array for performance/memory reasons.
 * Update the controllers cache to the new AS::Dependencies::ClassCache API.
   The original @controllers cache no longer makes much sense after @tenderlove's
   changes in 7b6bfe84 and f345e238.
 * Use TS::Cache in the connection pool to avoid locking overhead.
 * Use TS::Cache in ConnectionHandler.

This reverts commit 33b29e01, reversing
changes made to ac8c7293.

Reason:

https://github.com/rails/rails/pull/4684#commitcomment-920313

* I guess this would be the preferrable default for Bundler
* current version of Bundler converts :rubygems into 'http://rubygems.org', not https://,
  and that will help those who are working on a very poor network environment that doesn't allow SSL

This reverts commit 0ecd4640.

This reverts commit 8d8fd131.

mysql 2.8.1 gem can be built on ruby 2.0.0-preview1.

voloko/sdoc seems to be maintained again, in particular
the issues that made us fork it are resolved.

This reverts commit 7b290ad1.
debugger gem is now working ok with p286

Removing JSON for other ruby

"~> 2.2.2" from "~> 2.1.1". Also converted all hash rockets in the
Gemfile to the 1.9 syntax.