[Zope-CMF] Added a (temporary) collector classification

[Jens Vagelpohl]

To make it easier to identify issues deemed a release blocker for CMF  
2.0 I have added another classification to the collector, "CMF 2.0  
release blocker". It is intended for all issues that must be resolved  
before CMF 2.0 is released in its final form. It won't be used as a  
pool where people put their pet issue, just as a "admin" tool for  
supporters to classify issues that really are important for 2.0.

jens