Instead of repeatedly outputting the same identical messages across
multiple packages and repeating them all for every package after they
were all installed: just output the identical messages in the final
caveats output instead.
- Both formulae and casks can have caveats, but only formulae caveats
were shown at the end of a bulk install/upgrade/reinstall operation
via `Homebrew.messages.record_caveats`. This fixes that to show Cask
caveats too, for consistency (scrolling up all of the
multi-formulae-and-casks output to see caveats is time-consuming and
users might miss them).
- In doing this I had to change how `Messages#record_caveats` works
since the cask name is just a string, not an object.
