forEachUntil

[Brian Goetz]

Based on further user feedback, I think the name forEachUntil is too 
confusing; it makes people (including some members of this expert group) 
think that it is supposed to be an encounter-based limiting operation, 
rather than an externally-based cancelling operation.  Until seems to be 
inextricably linked in people's minds to encounter order, with all the 
attendant confusion.  People seem more able to understand cancellation, 
and in particular to understand that cancellation is usually a 
cooperative, best-efforts thing rather than the deterministic 
content-based limiting that people have in mind.

Accordingly, I think we should rename to "forEachWithCancel", which is 
more suggestive (and, secondarily, the ugly name subtly reinforces that 
it serves uncommon use cases.)