Log the rejected listener notification task under a dedicated logger name.

- Fixes #2166
- Some user applications are fine with the failure of notification
Fix indentation
Simplify exec-maven-plugin configuration

- Move the version number to the parent pom's pluginManagement section
- Remove unnecessary system properties
- Increase the scope of execution from compile to runtime
(Kind of) skip autobahn testsuite on -DskipTests

- autobahntestsuite-maven-plugin does not provide a way to skip all
  tests, so we run only one simple test when -DskipTests is set
Use smaller number of boss threads in the example

.. because usually there's no need to use many boss threads.
[#2215] DefaultChannelHandlerContext tasks needs to be volatile to ensure every thread only see full initialized instances
Add 'coverage' profile that generates the test coverage report
Prefer interface to implementation in type declaration

This fixes the build failure with JDK 8 due to animal sniffer error
Fix the compilation error in ConcurrentHashMapV8 + JDK8
Fix a build error

which occurred when -Pcoverage was not specified
[#2212] Skip autobahntestsuite when using -DskipTests
Fix a build error related with NPN version and JDK8
Remove a version clause added by mistake
Remove the StringCache option which was removed in JDK8
[#2219] Fix javadocs of HttpObjectAggregator to show correct handler order in pipeline
Merge branch 'master' of https://github.com/netty/netty