Fix "lost" files for iPhone/iPad/iPod Touch

[Bastien Nocera <hadess hadess net>]

Heya,

This patch fixes an apparent data loss:
https://bugzilla.gnome.org/show_bug.cgi?id=638191

It uses code similar to the same code in the Samba backend, and avoids
the file moving in the tree when renaming it. Was tested by myself and a
libimobiledevice maintainer.

OK to commit?

Cheers