Update to Checkstyle 6.1.1
Fixed trailing whitespace in changelog file.

Merged r1643121 from tomcat/trunk.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc8.0.x/trunk@1643205 13f79535-47bb-0310-9956-ffa450edef68
Fix concurrency issue identified while investigating BZ 57252. Ensure that non-container threads can't change the async state until the container thread has completed post-processing.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc8.0.x/trunk@1643215 13f79535-47bb-0310-9956-ffa450edef68
Follow up to r1643215. If something goes wrong, ensure non-container threads are unblocked.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc8.0.x/trunk@1643217 13f79535-47bb-0310-9956-ffa450edef68
Add whitespace to align flags to make it easier to see which states set
which flags.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc8.0.x/trunk@1643230 13f79535-47bb-0310-9956-ffa450edef68
Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=57252
Provide application configured error pages with a chance to handle an
async error before the built-in error reporting.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc8.0.x/trunk@1643232 13f79535-47bb-0310-9956-ffa450edef68
Merged revision 1643249 from tomcat/trunk:
Use the correct constant for the debug message.


git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc8.0.x/trunk@1643250 13f79535-47bb-0310-9956-ffa450edef68