Move pkg_symlink_cksum prototype to more proper header
Turn off broken incremental update for now.

We now have no stable builds and using of manifestdigest was wrong
in terms of repository update. For now, turn off incremental logic and always
update the full remote repo.
Add another useful example: unmaintained packages

In times before pkg(8) you had to jump through loops to get a list of
unmaintained packages on your system.
Fix spelling.

Update last-modified date.
Merge remote-tracking branch 'upstream/release-1.3' into release-1.3