Upgrade bundled Tomcat due to security vulnerabilities

There are some Tomcat security vulnerabilities reported against the bundled version 7.0.32:
CVE-2013-2067
CVE-2013-2071
CVE-2012-3544 - Not reported for Tomcat 7.0.32

Stash should be bundled with the latest Tomcat version 7.0.40 to ensure it contains a fix for the above security vulnerabilities.