Valgrind

I recall hunting for this last time I used Valgrind but it was far more complex than that. I should perhaps add that when I say that the message was repeated many times, it's 8-10 times and not thousands so it's clearly not every single node object that fails.

Anyway, after many hours of debugging today my theory is that it's nodes created by debug_mkconstantsvaluenode() in las.c that are suspect, but I haven't been able to zero in on exactly why. It seems like the pike_type structure may be polluted by invalid bits, but whether that's harmless or not I don't know. (Maybe like type/subtype false positives in svalues a long time ago.)

I feel I'd better let Mast or Grubba venture on from here into the belly of the beast... :-)