calchash(): use type_info::name() instead of tinfo().

calchash(): use type_info::name() instead of tinfo().

Custom RTTI considered harmful, part 4.

The hash value of the object of different types should be different whenever
possible. Hence calcash() needs a unique per type number. Previously we used
tinfo_key for this. typeinfo::name() (a *pointer* to implementation dependent
string) is also unique for each class, so it's just as good as tinfo() is.