* ORC: prepare for another patent-pending optimization
* bugfix
* '=copy' for refs can take a cyclic parameter for more ORC optimizations
* ORC: exploit the common 'it = it.next' pattern
* can't hurt to check for nil
* use an algorithm that is not obviously broken
* restore the test case
* final cleanups for --gc:orc
* cycle collector: new implementation
* cycle collector: make self-adaptive based on its previous effectiveness
* cycle collector: added Lins's jump stack to improve traversal from 3*N to 2*N
* cycle collector: make tests green
* API extensions and bugfixes
* code cleanup and use --gc:orc for tasyncawait
