Support more kindly for after method

[namusyaka]

ref #1240

The current implementation is going to try to return after_response if after_response is not false.
I guess the behavior is not expected, and users will be confusing.
Thoughts?

[dblock]

I think we would be trying to do too much for the user here. There should be a contract since this is an API. Right now it says you need to return a Rack compatible response from after, and I think we shouldn't be having code at runtime trying to "help" API authors work around that.

I vote to close this without merging, lets leave it here for a bit see if others think strongly otherwise.

[namusyaka]

Now, we must avoid returning value except false or nil on filters. I guess the constraint is very confusing. Thoughts?

[dblock]

So if in after you return anything, that's what's returned from the API. I think that's OK, otherwise it feels too magical. Curious what others think.

I see what you mean though, but I think adding more "magic" to it isn't better.

[namusyaka]

@dblock Yeah I see. I came to conclusion that your opinion is reasonable, but I'd like to hear other opinions.