Add reflection information for presences

[dtribble]

In command-line, development, or debugging environments, it would be valuable to be able to get alleged type and method information for presences and remote promises. Currently, a failed dispatch can return the set of available operations on a presence as part of the error information, but it would be much better to be able to systematically get that information without inducing an error.

[warner]

+1, as long as it's not an attractive nuisance that developers might be tempted to rely upon.

[erights]

Done, with @warner's atttractive nuisance caveat since it won't have any integrity until we have auxiliary presence data. Closing.