Allow ctrl.before to prevent further processing of the request

[pluma]

A useful (but apparently unintended) use of ctrl.before is to impose access restrictions.

Currently the only way to prevent further processing of a request in ctrl.before is to throw an exception. But this yields a route handling error, which results in a stacktrace returned as plaintext response. This is less than ideal.

This change allows ctrl.before callbacks to explicitly return false to prevent any further processing of the request. As the response body can be accessed in ctrl.before callbacks already, this also provides a workaround for use cases requiring intercepting all supported HTTP verbs in a single function.

Returning false to prevent further processing should be familiar to many JS devs from client-side event handling and libraries like underscore.

@moonglum, @fceller does this make any sense to you?

[moonglum]

Yes, it does.

[myguidingstar-zz]

the "returns false" feature has not been documented yet

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Edited: I was looking at master branch instead of devel. It is documented. Sorry for this