Merge pull request #622 from jrudolph/i/524/max-content-length

= can: after parsing error abort connection if other side doesn't also close in time, fixes #524
Merge pull request #618 from jrudolph/w/pipelining-limiter-waiting-on-acks

= can: always use acks for sending responseParts, PipelineLimiter now only responds to acks, fixes #617
= can: send Closed notifications to interested parties of all requests
! can: get rid of Http.Register.keepOpenOnPeerClosed, fixes #401

As discussed in the ticket:

client side
-----------

 - keepOpenOnPeerClosed = settings.sslEncryption
 - because the SslTlsSupport pipeline stage might be active but encryption
   still be disabled, we need to always actively close the connection whenever
   we see a PeerClosed event

server side
-----------

 - keepOpenOnPeerClosed = true
 - if no response is currently pending we can close the connection immediately
   when we see a PeerClosed event
 - otherwise, we let the last pending response close the connection