[Rivet] Rivet status update

[David Grellscheid]

Hi all,

To summarize the current status:

* All branches build fine again, checked on OS X and Linux with 
218640fbee89 (trunk) and aabf18dbe8a3 (release-2-0)

* The release-2-0 branch will become 2.1 after cleanup of the debris 
from yesterday and today and some more testing.

* I've merged the cuts branch into trunk, for use in 2.2 or later. I've 
verified that the cuts changes have not changed results in Herwig's LEP 
tests.

   David