Use pkgTagSection::Key in more places in src:apt

The speed critical paths were converted earlier, but the remaining
could benefit a tiny bit from this as well especially as we have the
facility now available and can therefore brush up the code in various
places in the process as well.

Also takes the time to add the hidden Exists method advertised in
the headers, but previously not implemented.

0 files changed, 0 insertions, 0 deletions