Rename SliceConcatExt::connect to join

[alexcrichton]

Tracking issue for rust-lang/rfcs#1102

[wesleywiser]

Hi, I'd like to take this if that's OK.

Should I also change all of the places in this repo where .connect is called to call .join instead? Or does that break bootstrapping?

Thanks!

[alexcrichton]

You should indeed! The stage0 libstd will have the rename so the bootstrap should be just fine (aka if make finishes then you're fine)

[wesleywiser]

Thanks! I'm working on this now.