[arch-general] Implement sql/sqlite database for pacman local database

[Alive 4ever]

I was curious why does 'pacman -Q' operations took longer than 'apt'
counterparts.  It seems that the local pacman databases are just
subdirectories with text files (desc, files) and gzipped text (mtree).
No wonder why local pacman databases tend to slow down over time and
need to be optimized periodically.

For long term pacman development road map, it would be better to use
single sql based database for tracking locally installed packages
instead of keeping directories of every installed packages.

This would provide faster access for local database as sql databases are
optimized for fast access.