Fix failure to retain value of allow_concurrency

- Also carry allow_concurrency value through to connection adapter
  (for postgresql)

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -97,7 +97,8 @@ module ActiveRecord
         if spec.kind_of?(ActiveRecord::ConnectionAdapters::AbstractAdapter)
           active_connections[active_connection_name] = spec
         elsif spec.kind_of?(ActiveRecord::Base::ConnectionSpecification)
-          self.set_connection ActiveRecord::Base.send(spec.adapter_method, spec.config)
+          config = spec.config.reverse_merge(:allow_concurrency => ActiveRecord::Base.allow_concurrency)
+          self.set_connection ActiveRecord::Base.send(spec.adapter_method, config)
         else
           raise ConnectionNotEstablished
         end

activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb

@@ -31,6 +31,7 @@ module ActiveRecord
       # multi-threaded access of the connection pools hash is synchronized.
       def allow_concurrency=(flag)
         if @@allow_concurrency != flag
+          @@allow_concurrency = flag
           if flag
             self.connection_pools_lock = Monitor.new
           else