CURLHandle cancel should talk to the multi

[samdeane]

CURLHandle cancel should talk to the multi and tell it to remove the handle - currently it sort of works the other way round, which means that you need access to the multi.

[samdeane]

The problem with this is that CURLHandle doesn't keep a reference to the multi.

Solutions:

• don't do it :)
• pass the multi in to cancel, and assume the default one if none was given
• ??