Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56717
Fix duplicate registration of MapperListener during repeated starts of embedded Tomcat.
Properly unregister it when Tomcat stops.

It is backport of r1610562.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1611495 13f79535-47bb-0310-9956-ffa450edef68
Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56717
Allow repeated Mapper.addHost() calls for the same host. E.g. if the host has been implicitly added by addContextVersion() call.

It is backport of r1610564.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1611496 13f79535-47bb-0310-9956-ffa450edef68