speed up startup (avoid loading some gems on startup)

correct group permission leaks
add Discourse.cache for richer caching support

lib/cache.rb

@@ -0,0 +1,55 @@
+# Standard Rails.cache is lacking support for this interface, possibly yank all in from redis:cache and start using this instead
+#
+
+class Cache
+  def initialize(redis=nil)
+    @redis = redis
+  end
+
+  def redis
+    @redis || $redis
+  end
+
+  def fetch(key, options={})
+    result = redis.get key
+    if result.nil?
+      if expiry = options[:expires_in]
+        if block_given?
+          result = yield
+          redis.setex(key, expiry, result)
+        end
+      else
+        if block_given?
+          result = yield
+          redis.set(key, result)
+        end
+      end
+    end
+
+    if family = family_key(options[:family])
+      redis.sadd(family, key)
+    end
+
+    result
+  end
+
+  def delete(key)
+    redis.del(key)
+  end
+
+  def delete_by_family(key)
+    k = family_key(key)
+    redis.smembers(k).each do |member|
+      delete(member)
+    end
+    redis.del(k)
+  end
+
+  private
+
+  def family_key(name)
+    if name
+      "FAMILY_#{name}"
+    end
+  end
+end