In rare cases, likely due to a well timed Ctrl+C, but possibly due to a
broken mirror, a ".part" file may have size at least that of the correct
package size.

When encountering this issue, currently pacman fails in different ways
depending on where the package falls in the list to download.  If last,
"wrong or NULL argument passed" error is reported, or a "invalid or
corrupt package" issue if not.

Capture these .part files, and remove the extension. This lets pacman
either use the package if valid, or offer to remove it if it fails checksum
or signature verification.

Signed-off-by: Allan McRae <allan@archlinux.org>