451529 Change sentinel class for finding jstl on classpath to  org.apache.taglibs.standard.tag.rt.core.WhenTag
452201  EnvConfiguration.destroy() should set the classloader
447472 Clear async context timeout on async static content
452424 Do not add Date header if already set
Merge remote-tracking branch 'origin/jetty-9.2.x'

Conflicts:
	jetty-http/src/main/java/org/eclipse/jetty/http/HttpFields.java
	jetty-server/src/main/java/org/eclipse/jetty/server/HttpChannel.java
	jetty-server/src/main/java/org/eclipse/jetty/server/handler/ResourceHandler.java