When adding a new unknown hostmask to the message history accounts, we now
take significant advantage of the aliases table to find an existing account
id for the hostmask before assigning it a new account id.
Likewise, we now take significant advantage of the aliases table when looking
for a nick-change match.
Fix misc channel case-sensitivity issues, add missing last-seen hostmask
updates, reduce message account linking log verbosity level.
8ba4ffffe4