bugfix: allow loading of external xml entities

on Ubuntu 14.04, tomcat 7.0.52 would throw this error on startup:
java.io.FileNotFoundException: Could not resolve XML resource [null]
with public ID [null], system ID [web-mime-mappings.xml] and base URI
[file:/opt/tomcat/sites/paxdb_1/tomcat/conf/web.xml] to a known, local entity