Cache invalidation problem

[rlander]

Suppose you have a Greeting model with [id, text] and you want to list all available greetings.

5> boss_db:find(greeting, []).
[{greeting,"greeting-8",<<"Hello">>}, {greeting,"greeting-9",<<"Foo">>}]

You have caching enabled and update a Greeting field like so:

6> Greeting = boss_db:find("greeting-9").
(Greeting:set(text, "Bar")):save().
{ok,{greeting,"greeting-9","Bar"}}
7> boss_db:find(greeting, []).
[{greeting,"greeting-8",<<"Hello">>}, {greeting,"greeting-9",<<"Foo">>}]

The cache for the first query should be invalidated but it won't. #260 fixes this.