Move pkg_symlink_cksum prototype to more proper header
Add a pkg_symlink_cksumat to fix pkg-delete

Issue:	#913
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.
Merge pull request #930 from blabber/master

Add another useful example: unmaintained packages
Fix spelling.

Update last-modified date.