When the copying of a file is interrupted (by the user or by some error) an
incomplete file is left of the target folder. It is not possible to detect that
this file is incomplete at first glance.

Test case:
 - Open Nautilus
 - Open a second folder on a tab
 - Copy/move a big file form one tab to another
 - Cancel the transfer using the X button.

The unfinished file remains on the destination folder, now, since this file is incomplete (possibly unusable) and the user directly stated that he/she did not want to transfer this file, seems wiser to remove the incomplete file.

If for some reason is not possible to delete the incomplete file, Nautilus should have a mechanism to inform the user the file is not complete (ex: adding an extra extension to the filename).

See also: https://bugs.launchpad.net/hundredpapercuts/+bug/1072135
2.6.x branch report: https://bugzilla.gnome.org/show_bug.cgi?id=403652