[eclipselink-dev] Fix for 271359 checked in

[christopher delahunt <christopher.delahunt@xxxxxxxxxx>]

https://bugs.eclipse.org/bugs/show_bug.cgi?id=271359

fix for bug 271359 - "NullPointerException caused from multiple threads 
calling find on the same class"
Changes: CMP3Policy changed to initialize with the descriptor instead of 
lazily when accessed.
Manually tested in concurrent load app that initially showed the error.  
Reviewed by Gordon Yorke