[FIXED JENKINS-19171] Identify user agent for Internet Explorer 11.

See discussion in [JENKINS-19171](https://issues.jenkins-ci.org/browse/JENKINS-19171). Updating YUI (to something _after_ 3.11.0) might be better, but this is a relatively conservative change.

I manually ported the change to `yahoo-min.js`; is there a better way?