plugin debug trace output

[Walt Karas]

FYI, this is a way to make your (non-core) plugin build with the new (much
lower overhead) debug interface, or the old one if the the new one is not
available in the ATS version you need the .so to run with:

#if defined(TSDbg)

const TSDbgCtl *dbg_ctl_yada = TSDbgCtlCreate("yada");
#define DBG_YADA(...) TSDbg(dbg_ctl_yada, __VA_ARGS__)

#else // For obsolete release of TS.

#define DBG_YADA(...) TSDebug("yada", __VA_ARGS__)

#endif