Upgrade JIRA standalone version to Tomcat 5.5.15 (synch with Confluence and for reuse buffers option)

To take advantage of the -Dorg.apache.jasper.runtime.BodyContentImpl.LIMIT_BUFFER=true flag (for JRA-10145), we need to upgrade Tomcat. Since Confluence use Tomcat 5.5.15, that seems like a good target.

Release notes show that this flag was not added until 5.5.15 anyhow:

http://tomcat.apache.org/tomcat-5.5-doc/changelog.html