Give better error messages on database locking failures

This was noted when trying to perform an operation on a pacman database
on a read-only file system. Print the actual underlying errno string,
and only show the "you can remove" message if the lock file actually
exists.

Before:
    $ pacman -Su
    error: failed to init transaction (unable to lock database)
      if you're sure a package manager is not already
      running, you can remove /e/db.lck

After:
    $ pacman -Su
    error: failed to init transaction (unable to lock database)
    error: could not lock database: Read-only file system

Signed-off-by: Dan McGee <dan@archlinux.org>

0 files changed, 0 insertions, 0 deletions