Hi,

I'm currently trying to write some code based on the pdb2hpp example.
I'm having trouble detecting/reconstructing pure virtual methods correctly. It seems it's not possible to check for the pureintro (0x06) property only, like it's possible with the purevirt property (0x01):
https://github.com/willglynn/pdb/blob/7c35c3c82fe42a0aa505c0715d57f68ee93196fb/src/tpi/data.rs#L627

What's the reason behind this merge (between property 0x04 and 0x06)? Am I missing something?