Update to latest dynapath

0.2.3 has a fix that prevents pomegranate from modifying the boot
class loader.

The ExtClassLoader is a URLClassLoader, but shouldn't be given jars
containing classes that it has already loaded via another url.

Apparently the code in the old pomegranate protocol implementation
that extended ExtClassLoader wasn't really a no-op. 

0.2.3 isn't yet on central - I'll comment here when it lands.