Progress on the Gilectomy

[Paul Rubin]

I always thought the GIL removal obstacle was the need to put locks
around every refcount adjustment, and the only real cure for that is to
use a tracing GC.  That is a good idea in many ways, but it would break
the existing C API quite seriously.  Reworking the C modules in the
stdlib would be a large but not impossible undertaking.  The many
external C modules out there would be more of an issue.