Added atomic target word sized field to track missed event count.
Added atomic target word sized field to track missed event count.

This should yield better performance for applications that never
receive any messages, instead of having to lock a mutex just to
check the count of missed messages when trying to send.

tomaka/android-rs-glue,tempbottle/android-rs-glue,ozkriff/android-rs-glue,skligys/android-rs-glue