use named enum for TypeInfo_Struct and TypeInfo_Class m_flags
use named ClassFlags enum in _d_newclass
disable finalization for extern(C++) classes

- They lack the classinfo pointer at vtbl[0] so the GC
  can't currently can't finalization.

- We could probably put the classinfo at vtbl[-1] though
  that would collide with C++ RTTI, any other ideas?
Merge pull request #614 from dawgfoto/noFinalizeCPPclass

disable finalization for extern(C++) classes