print asset:precompile --trace output if can't detect rake task

lib/language_pack/rails3.rb

@@ -61,10 +61,21 @@ def run_assets_precompile_rake_task
             puts "http://devcenter.heroku.com/articles/rails31_heroku_cedar#troubleshooting"
           end
         end
+      else
+        if asset_pipeline_rails?
+          puts " ! Error running/detecting assets:precompiling task. Rerunning with --trace"
+          pipe("env PATH=$PATH:bin bundle exec rake assets:precompile --trace 2>&1")
+        end
       end
     end
   end
 
+  # detects if the rails we're using has the asset pipeline
+  # @return [Bundler::LazySpecification] the matching gempsec for rails if true and nil if it isn't compatible
+  def asset_pipeline_rails?
+    lockfile_parser.specs.detect {|spec| spec.name == "rails" && spec.version >= Gem::Version.new("3.1.0") }
+  end
+
   # setup the database url as an environment variable
   def setup_database_url_env
     ENV["DATABASE_URL"] ||= begin