[Rivet] Pluggable analyses branch

[Andy Buckley]

Hi Rivetters,

I've implemented a form of dynamic analysis loading for Rivet, which you 
might be interested in. You can browse/checkout the branch from SVN at:
http://svn.hepforge.org/rivet/branches/pluggable-analyses/
and
svn+ssh://svn.cedar.ac.uk/svn/hepforge/rivet/branches/pluggable-analyses

I think this approach is the way forward - it eliminates the fiddly 
analysis name enums, simplifies some aspects of how analyses are 
registered with the analysis handler, and of course makes it easy to add 
new analyses without needing to recompile/reinstall Rivet. That will 
help Genser among others - ATLAS RTT?

At the moment the code in the branch is set up to try and load analyses 
from .so files found in the dirs listed in LD_LIBRARY_PATH, 
RIVET_ANALYSIS_PATH and the current directory. I'll also get it to 
search the Rivet libraries install directory, since that's where the 
standard analyses will be found and it would be nice not to have to set 
any env vars for it to work.

That's all - it would be helpful if some people would take a look at it 
and offer some feedback (especially if you're not using a Linux system - 
it won't work, but help on getting it to work would be good!). If all is 
okay, I'd like to merge to the trunk pretty soon.

Andy