[FLOW] Memory Leak: Invalid continuations tree after using invalidation

[Vadim Gritsenko <va...@reverycodes.com>]

Hey all,

Found out today that once you use wk.invalidate() on continuation, 
following continuations will still get created under the invalidated 
continuation. This should cause memory leak, because invalidated 
continuation is not part of the continuations forrest anymore, and all 
its newly created children will not be accessible through continuations 
forrest, and won't get invalidated when you call invalidate() on the 
tree root continuation.

I'll try and fix this one, but I'm not sure that my fix will be elegant 
- please feel free to change this fix.

Vadim