marshal cannot serialize standard Maps

[DavidBruant]

This came out in a discussion with @katelynsills about what the getAvailableTickets method could return in the Opera ticket contract

[erights]

For now, we can't serialize any kind of maps. For now though, given a map m, you can turn it into an array of [key, value] pairs by

[...m]

which we can serialize. On the other side, given an array of [key, value] pairs pairs, you can turn it back into a map by

new Map(pairs)

Longer term, in the https://github.com/Agoric/agoric-sdk/tree/passable-collections branch I'm working on passable collections which can be marshalled and unmarshalled correctly, and whose key-lookup-equality is sameStructure equality, which is the equality preserved by our marshal and distributed object semantics. But this won't happen soon.

[erights]

The need for passable collections is already described or started in other issues and PRs. The so-called "passable collections" would include passable sets and passable maps. However, that's as far as this support should go. Marshal should not serialize standard sets and maps. Since the others remain open I'm closing this.