This thread is similar to: Disable taglib scanning in google app engine (Jetty)
The author of that thread accepted a wrong answer.
We were trying to reduce the
Posting my comment from above as answer:
Rename your JARs to match the NoTLDJarPattern used by AppEngine's webdefault.xml.
It's not pretty, but naming all your JARs e.g. jetty-(...).jar should prevent them from being scanned for TLDs.
Alternatively, repackage all JARs into one big JAR and just give that a name covered by AppEngine's NoTLDJarPattern.