[4.3] Upgrade To Predis 1.0

This was actually surprisingly simple. I've been through the changes in 1.0 with a fine-tooth comb, and noticed one small error affecting both predis 0.8 and 1.0; see #5156.

NB: predis 1.0 will be released in ~10 days time, so if you want to wait for a stable release before merging, it shouldn't be long now.