(maint) pin i18n

activesupport calls in the latest i18n, which drops support for Ruby
1.8.7 and breaks acceptance tests on Ubuntu 12.04.  This PR pins to a lower
version with 1.8.7 support.
Merge pull request #1188 from wkalt/maint/pin-i18n

(maint) activesupport calls in the latest i18n, which drops support for ...
Merge branch 'stable'

* stable:
  (maint) pin i18n

Conflicts:
	acceptance/setup/pre_suite/40_install_deps.rb
(PDB-353) Don't add new mbeans for metrics URLs.

- Added a check to ensure that requests for metrics/mbeans information
  do not cause creation of additional mbeans to track the metrics URLs.
  We check specifically for the "available mbeans list" URL, and for any
  specific metric URL from that list.
- Added test code to verify that :timers and :meters are not created
  when metrics-related URLs are accessed.