trace: reimplement the DTRACE function so it doesn't use a vector

One question I have about this stuff is if I should call everything trace, or debug?  This diff is somewhat confused about that (some things are trace and some things are debug) and I expect to fix it. We always called this stuff "trace flags" in the past, but we I would like to start using these flags for other things.  For example, turning on and off debugging breakpoints of different kinds.  Execution tracing is a totally different mechanism but does use trace flags.  My personal inclination is that trace flag is probably a bad name, but perhaps debug is a bad name too.  Just call it "flags"?  Or SimFlags?