Fixed #3386.
Merge pull request #3397 from cgaebel/issue-3386

Fixes #3386.
Try to unbreak the build by removing unused import
Remove most of FlowList

This needs to be reworked for DST.  Until then, DList<FlowRef> will do.
Upgrade to rustc 0.12.0-pre (4d2af3861 2014-09-17 15:51:11 +0000)