Notification Rule meta data being saved to all post types

[frankiejarrett]

A user reported in the plugin forum that they were seeing strange post meta appearing on their posts.

triggers: a:0:{}
groups: a:0:{}
alerts: a:0:{}

I believe this is being caused by the save_post action in WP_Stream_Notifications_Post_Type not properly limiting itself to only adding meta information to Notification Rule posts.

[frankiejarrett]

Here is a gist that will remove the unwanted meta from all other post types: https://gist.github.com/fjarrett/be5423e0899895558d75