bug#22865: 25.0.91; Use Proof General with emacs-25 on OS X frequent hangs coqtop

[John Wiegley]

I'm afraid this could be difficult to debug, but here is my scenario:

 1. Open a .v (Coq) file within my project.

 2. Ask Proof General to evaluate the file to the end.

 3. Before a certain definition, PG will hang waiting on a response from
    "coqtop", the evaluator. Checking the process list shows that this
    process is not doing anything.

 4. Once this happens, C-g or C-c C-c to abort the evaluation leaves me
    in a broken state where nothing can evaluate anymore. The only
    recourse is to "killall coqtop", and then attempt the evaluation
    again. However, the same definition always causes it to hang. There
    is no common factor about the definitions that I can see, but it
    happens reliably every time for each file where it does occur.

if I switch to 24.5, everything evaluates fine. It happens quite
frequently with emacs-25, but never with 24.5.

Now, this could be 25.1, or it could be Mac port vs. NeXTstep, or it
could be some other subtle interaction with my environment.

Unfortunately this will take time to narrow down, and I have to get the
Coq code written, so for now this is a placeholder and I must revert to
using 24.5. I hope to come back to this later, especially if others have
ideas on where to look.

John