Use std::atomic family
Use map::emplace instead of inserting std::pair (C++11)
Ensure delegate is retained
Put posix_spawn related failure in crash report
Don’t close file descriptor until after ~PackedFdMessageReader()

The message reader may use the file descriptor in its destructor, which is why we can’t close it until that object has been destroyed.
Reject bundle index cache if version is not the current
Update to Cap’n Proto v0.3.0