added the ability to limit memory consumption of code submissions executed using Docker

db/migrate/20150317083739_add_memory_limit_to_execution_environments.rb

@@ -0,0 +1,11 @@
+class AddMemoryLimitToExecutionEnvironments < ActiveRecord::Migration
+  def change
+    add_column :execution_environments, :memory_limit, :integer
+
+    reversible do |direction|
+      direction.up do
+        ExecutionEnvironment.update_all(memory_limit: DockerClient::DEFAULT_MEMORY_LIMIT)
+      end
+    end
+  end
+end