Comment 3 for bug 1732518

This debdiff re-introduces the forwarding code, it also cleans a number of things up:

 - It fixes a regression of apport on systems using upstart
 - It replaces the is_container logic with a is_same_ns function that lets us check things more carefully.
 - If the pidns differs but mntns doesn't, apport will process the crash locally, using the global pid.
 - If the mntns differs but pidns doesn't, then the crash is just plain ignored
 - If pidns and mntns differ and an apport receiver socket can be found, the crash is forwarded. If none can be found, the crash is ignored.
 - All arguments except the first and last are now sent to the receiver.
 - The receiver has a check for the number of received arguments, ignoring any crash that doesn't match its view of the world.
 - The ucred is used for pid passing, translating the pid across pidns.

I've done the following tests:
 - Standard crash on host => crash in /var/crash of host
 - Crash on host in a different pidns => crash in /var/crash of host
 - Crash on host in a different mtnns => no crash file
 - Crash on host in a different pidns and mntns => no crash file (no receiver found)
 - Crash in container with receiver setup => crash in /var/crash of container