Add a human readable error when failing to attach to SHM
Ensure an out-service frame is consistent for the RDP peer

This patch ensures that a BEGIN_UPDATE / data / END_UPDATE sequence
sent by the out-service will be treated as a frame in the frontend thread.
To do this we differ the feeding of the order queue if all the messages for
a frame aren't arrived yet.
Merge remote-tracking branch 'hardening/frame_consistency'