Use a more correct algorithm for the global pool block list
Use a more correct algorithm for the global pool block list

The previous algorithm contained a data race which could cause some
nodes of the list to be incorrectly discarded.

ponylang/ponyc,ponylang/ponyc,CausalityLtd/ponyc,jemc/ponyc,sgebbie/ponyc,jemc/ponyc,mkfifo/ponyc,boemmels/ponyc,cquinn/ponyc,kulibali/ponyc,dipinhora/ponyc,mkfifo/ponyc,sgebbie/ponyc,Perelandric/ponyc,Praetonus/ponyc,dipinhora/ponyc,dipinhora/ponyc,kulibali/ponyc,Perelandric/ponyc,Theodus/ponyc,CausalityLtd/ponyc,Theodus/ponyc,mkfifo/ponyc,Perelandric/ponyc,Theodus/ponyc,sgebbie/ponyc,cquinn/ponyc,cquinn/ponyc,mkfifo/ponyc,Theodus/ponyc,Perelandric/ponyc,Perelandric/ponyc,boemmels/ponyc,kulibali/ponyc,sgebbie/ponyc,boemmels/ponyc,Praetonus/ponyc,boemmels/ponyc,Theodus/ponyc,Praetonus/ponyc,sgebbie/ponyc,Praetonus/ponyc,ponylang/ponyc,boemmels/ponyc,cquinn/ponyc,kulibali/ponyc,mkfifo/ponyc,jemc/ponyc,CausalityLtd/ponyc