Temporarily set uid_ndx in the delete code if the transfer is not

Temporarily set uid_ndx in the delete code if the transfer is not
preserving ownership, but we want to know what the UIDs are on the
files we're deleting.  Changed the DEL_OWNED_BY_US flag to be
DEL_NO_UID_WRITE, which is only set when a file is owned by us and
we can't write to it.  Fixed a glitch in the error handling of the
--delete-delay code where it might try to enable delete-after in
incremental-transfer mode.  Made a simple (well tested) optimization
in the --delete-delay code and a few other readability changes.