trying a DependingPromise constructor

to resolve with pending promises, that should take care of cancellation
and forward subscriptions intelligently

* cancellation is untested, might not work
* something is buggy, A+ testsuite fails
* rejecting when cancelling is totally ugly
* .chain() still cannot be simplified as much as I'd like to
* the new constructor currently has only the .chain usecase,
  I'm not sure whether it needs to be an extra constructor
use AdoptingPromise from DependingPromise (for non-forwardable handlers)
adopt/assimilate return proper continuations, +ContinuationBuilder.forkMany
fix forkMany, some improvements to runHandlers and fork
[minor] accurate warning messages for adapter
Idea for non-strict forking of continuations

Lazyness, here I come!
first draft, not really working
Prevent double-execution of asynchronously scheduled continuations

* Promise.runAsync now returns a more-or-less safe continuation
  that will unschedule `cont` when being run before the async one
* AdoptingPromise/fork does collect all handlers again, not only their tokens,
  but adopt will continue only those subscriptions that have the .lazy
  flag set to false (after their fork() continuations have been called)
  The other subscriptions stay lazy and can be continued by their fork()
  continuation
* the fork() continuations no longer throw when called multiple times,
  but just ignore it (hopefully making them safe)
- yet the go() continuation still is handed out multiple times
* A+ testsuite passes again
[bugfix] Promise::mapError did not reject, +naming some functions
some cleanup and docs, docs, docs\!
Different adoption style with follow instead of proceed

* cleaner code for directly executing the handlers of follower promises:
  adopt() now returns the strict handlers,
  and is passed as .follow instead of .proceed
* direct resolution (e.g. when cancelling) of an AdoptingPromise got more
  ugly: new ResolvedPromise.fork({follow: adopt})
  and depends on fork to execute the followers immediately
* I fear at some point I will need (want?) to give direct access to the
  handlers array from within a resolver function
* This seems to have a better complexity than DependingPromise
Merge artefacts from branch 'promise-depending' into promise-lazy-continuation

Conflicts in
	promise/Promise.js
	promise/todo.md
were resolved. Actually, nothing of DependingPromise itself is left, but some
fixes and snippets from that branch were useful.
Merge branch 'promise-lazy-continuation'