This series, brought to you by Yahoo! Finance, looks at which upgrades and downgrades make sense and which ones investors should act on. Today, we'll be examining a trio of rating changes in the optical networking business as RBC Capital throws its support behind Finisar ( FNSR ) and withdraws it from rivals Ciena ( CIEN 2.66% ) and JDS Uniphase ( VIAV 2.64% ). Let's dive right in, beginning with...