Fix by Constantin Loizides

I had problems using ImportParticles
with the "Final" option. When writing
the "particle" branch with TTree::Fill
it crashed whereas when using the "All"
option the same macro work (macro is attached).
Looping over the particles in the TClonesArray
works perfectly in both cases
(particles->Print()).

I "solved" the problem  changing the
TPythia6::ImportParticles in the following way:

The dummy index i is always incremented regardless
whether a particle was "final" or not. Introducing a
variable which  actually counts the particles that
were inserted into the TClonesArray apparently works


git-svn-id: http://root.cern.ch/svn/root/trunk@5446 27541ba8-7e3a-0410-8455-c3a389f83636