Fix for clearcase and enhancment to date labeller

I suspect this isn't in the right format (it would probably have been better to have separate pull requests for these 2 things) but this is my first attempt at using github and my first pull request, and now that I've pushed those changes I'm not sure how to make my github fork look different.

There are 2 changes here:
1) A fix for missing Clearcse defaults, which causes issues if the clearcase element isn't specified. (I no longer have access to the cruisecontrol.net environment where I tested this).

2)  An enhancement to the date labeller to add an incrementOnFailure attribute option that I originally created for ccnet 1.4 and have been merging into new ccnet versions. It allows you to have the date labeller leave the failed builds instead of overwriting them.

Mike