This fixes a really bad bug that seems to have been there for a while. Canceling
a nsock connect SSL operation fails with fatal(). I have never seen it in real
life though.
Added a corresponding unit test.
This prevents nsock from iterating over the whole list of events at
each runloop, thus improving performance.
It made it necessary to have pointers from the msevents to the event
lists they belong to. The patch therefore also changes gh_list from
autonomous containers to embedded structures.
Added unit tests accordingly and cosmetic changes to make things look
more consistent.