Particle Generator Bugfixes

A very kind (and smart) reader sent in a handful of bugfixes for my iPhone particle system, including a fix for the bug that was causing the test application to freeze. I believe those fixes also solve the problem with deleting particles, so I can put back in the code I had written and then removed that freed up the particle memory when a generator no longer has any visible particles. Will probably be a few weeks before I can get to doing that, though.

Thanks WG! That was a huge help.