duplicated --itemize-changes hangs since 3.1.1pre1

[Carlos Carvalho]

One of our rsync updates has been getting stuck at the download point.
It gets the incremental list, deletes stuff but when it tries to
download new/updated files it gets stuck and aborts after the timeout;
it doesn't even create the temporary. Experimentation shows that it
happens because the --itemize-changes option is repeated (on purpose);
putting it only once works normally. Apparently it's been happening
since 3.1.1pre1, and continues with 3.1.1 downloaded from git today
(July 5).

It only happens with one of the many upstreams we use(!); protocol
version is 30. Bizarre...