Add some notes

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1615687 13f79535-47bb-0310-9956-ffa450edef68
Remove references to the deleted system property. Document the current default.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1615693 13f79535-47bb-0310-9956-ffa450edef68
When the gzip option is enabled for the DefaultServlet ensure that a suitable Vary header is returned for resources that might be returned directly in compressed form.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1615697 13f79535-47bb-0310-9956-ffa450edef68