Only silence I18n deprecation warning if attr exists.

Fixes #1950.

Gemfile

@@ -23,6 +23,10 @@ group :development do
   # For the integration tests
   gem "diffy"
 
+  # Lock the current lowest requirement for ActiveSupport 3 to ensure we don't
+  # re-introduce https://github.com/CocoaPods/CocoaPods/issues/1950
+  gem 'i18n', '0.6.4'
+
   gem 'mime-types', '< 2' # v2 is 1.9.x only
   gem 'coveralls', :require => false
   # Explicitly add this, otherwise it might sometimes be missing:

Gemfile.lock

@@ -7,7 +7,7 @@ GIT
 
 GIT
   remote: https://github.com/CocoaPods/Core.git
-  revision: 76c726cb88ec60dc64c62e2a87b1845319e84569
+  revision: 7af0d1097b00248e37576101f9330cb959fb5f9f
   branch: master
   specs:
     cocoapods-core (0.30.0)
@@ -109,7 +109,7 @@ GEM
     ffi (1.9.3)
     fuzzy_match (2.0.4)
     github-markup (1.1.0)
-    i18n (0.6.9)
+    i18n (0.6.4)
     json (1.8.1)
     json_pure (1.8.1)
     listen (1.3.1)
@@ -173,6 +173,7 @@ DEPENDENCIES
   coveralls
   diffy
   github-markup
+  i18n (= 0.6.4)
   kicker!
   mime-types (< 2)
   mocha

lib/cocoapods.rb

@@ -9,7 +9,10 @@ require 'active_support/core_ext/string/inflections'
 require 'active_support/core_ext/array/conversions'
 # TODO check what this actually does by the time we're going to add support for
 # other locales.
-I18n.enforce_available_locales = false
+require 'i18n'
+if I18n.respond_to?(:enforce_available_locales=)
+  I18n.enforce_available_locales = false
+end
 
 module Pod
   require 'pathname'