Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=49779

Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=49779
Improve handling of POST requests and FORM authentication, particularly when the user agent responds to the 302 response by repeating the POST request including a request body. Any request body provided at this point is now swallowed.
Clean up the FormAuthenticator test case and extend the coverage to include bug 49779 and the remaining combinations of request methods.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@987955 13f79535-47bb-0310-9956-ffa450edef68