[0/10] threads for emacs

[Tom Tromey <tromey@redhat.com>]

Here is a somewhat different version of the threads patches for Emacs.

I finally admitted to myself that I will never find the time or mental
energy to update the complicated-but-efficient approach to let bindings
that I had originally planned.  Instead, this series implements
something much slower, but also simpler -- it conceptually unwinds the
bindings when a thread loses the global lock, and rewinds them when a
thread acquires the lock.  Hopefully some motivated person can improve
this situation.

I'm posting this now not because it is complete, but because it is
complete enough to be tried out and discussed.  I'm sure it has bugs.
It is also missing ChangeLog entries and documentation.  Plus I have a
to-do list...

I would appreciate your reasoned comments.

Tom