Move and swap operators

[graydon]

Add operator <- for move semantics and operator <-> for in-place swapping. Essential components to making the unique ownership model work. Steal <- from send, turn operator send into |> and make it chain to the right.

[msullivan]

<- is in, but the typestate component doesn't exist yet. Receive is now |> but doesn't chain.

[msullivan]

Swap is implemented.

[graydon]

Is there much left to do here, aside from "fix bugs as they occur"?

[msullivan]

Tim has implemented the typestate stuff.
Currently we don't properly check that the arguments to swap are lvals and that the RHS of move is a local. The former will trip an llvm assert, the latter will compile and do the wrong thing.

Otherwise I think it should be good?

[graydon]

Heh. Ok. Want to fix those?

[msullivan]

The swap issue has been fixed in #590 and the move issue has been opened as #591.

I'm going to close this bug.