[Rivet] Small problem with the latest version

[David Yallup]

Hello,

I don't know if this has been reported but something I thought I should 
flag this up. I was helping someone set up the latest rivet install 
v2.5.1 on an SL6 machine, where the default python is v2.6.

Everything compiles "correctly", however when attempting to run 
rivet-mkhtml, it errors with the following:
ERROR: required program 'latex' could not be found. Exiting...

This is something that came in with rivet 2.5.0 I think (I've had 
earlier versions of rivet running on the same architecture), and is 
solved by using python2.7 (I think its something new in make-plots that 
doesnt play nicely with old python versions), but you then need to 
compile with python 2.7, so I'm wondering if compilation of rivet should 
be stopped if you are using python <=v2.6 as we do with the c++11 
headers now, or enforce some check on whatever feature make-plots is 
trying to use.

This is a fairly niche problem but I thought it was worth mentioning

Cheers,
David