[cmucl-imp] Snapshot 2018-10

The November snapshot has been tagged (snapshot-2018-10). Binaries will be uploaded soon. What's new: * New functions `SET-GC-ASSERTIONS` and `GET-GC-ASSERTIONS`. See the docstrings for more information and also ~~#69~~. Tickets: * ~~#69~~ GC assertions compiled in and allow user to enable them.