RFR: JDK-8076493 - DIO event needs to be processed inside 1 thread

[alexey karaksin]

issue: https://bugs.openjdk.java.net/browse/JDK-8076493
webrev: http://cr.openjdk.java.net/~amironov/8076493/

Please review the changes made to make all event processing functions 
run in the same thread - changes in EventQueue.java
Plus UART event processing changes in order to run correctly in case of 
1 event thread.

Regards,
Alexey