Improve makepkg config loading for checkpkg and extrapkg.

Now, checkpkg and extrapkg will fail if /etc/makepkg.conf doesn't exist, and will also try to load in personal user's settings in ~/.makepkg.conf

Signed-off-by: Travis Willard <travis@archlinux.org>
Signed-off-by: Aaron Griffin <aaronmgriffin@gmail.com>