phase1: use sha2rsync.pl for 'targetupload'

phase1: use sha2rsync.pl for 'targetupload'

This patch uses sha2rsync.pl to build a list of files to upload
to the remote server via rsync.

Because --files-from is taken as a literal list of files to consider by
rsync (the file list generation is skipped), it will not delete files on
the receiver.

To work around that without implementing a broken client-side upload
queue management system, 'targetupload' is split in two: the first step
uploads and updates new and existing files using rsync standard
mechanism, and the second step does nothing but delete files that are
present on the receiver but not on the sender.

As a side effect, this implements a '--delete-after' deletion style where
files are only deleted after uploads/updates finished successfully.

Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>