Return a set of token_ids from _babble (rather than a list)
Return a set of token_ids from _babble (rather than a list)

This matches the return type of _filter_pivots, the other
routine that returns potential pivot tokens.

LeMagnesium/cobe,pteichman/cobe,DarkMio/cobe,tiagochiavericosta/cobe,pteichman/cobe,DarkMio/cobe,tiagochiavericosta/cobe,wodim/cobe-ng,meska/cobe,wodim/cobe-ng,LeMagnesium/cobe,meska/cobe