dav: try copy and delete fallback if backup couldn't be created
dav: try copy and delete fallback if backup couldn't be created

Move operation fails immediately with G_IO_ERROR_CANT_CREATE_BACKUP if
G_FILE_COPY_BACKUP is specified. Consequently copy and delete fallback
isn't executed. Return NOT_SUPPORTED instead of CANT_CREATE_BACKUP to
proceed with the fallback if G_FILE_COPY_NO_FALLBACK_FOR_MOVE isn't
specified.

https://bugzilla.gnome.org/show_bug.cgi?id=740057

gicmo/gvfs,gicmo/gvfs,gicmo/gvfs,gicmo/gvfs