A few compiling issues

I had a few issues compiling, and these commits fix them. I'm not sure if perhaps there was an issue on my end with GEANT versions w.r.t. -Werror (I used 4.9.6.p03), so maybe someone can confirm.
Aha -- it should be `Rtypes.h`, not `RTypes.h`. (Why, oh why, would anyone make a case-insensitive file system?) It probably worked without it because everything that included `PMT.hh` had already included `Rtypes.h` first.