taglist: avoid pointless tag name -> quark lookups

taglist: avoid pointless tag name -> quark lookups

We never get a tag name quark from a caller, it's always a
string, from which we'll try to look up our tag info in the
hash table, so change the hash table key from quark to string.
Avoids a bunch of pointless string => quark lookup in the
global quark table. We need to do an extra string => quark
conversion now when we copy a taglist, but in that case we're
in a slow path anyway.