varnishadm and pipe

https://www.varnish-cache.org/trac/ticket/1314

Hi dev!

"man varnishadm" say something like:

---
EXAMPLES
       Some ways you can use varnishadm:

       varnishadm -T localhost:999 -S /var/db/secret vcl.use foo
       echo vcl.use foo | varnishadm -T localhost:999 -S /var/db/secret
       echo vcl.use foo | ssh vhost varnishadm -T localhost:999 -S /var/db/secret
---

unfortunately, piping to varnishadm does not work anymore.
I think it is useful to do something like:

cat myHugePurgeList |varnishadm -S secret

But it enters in a infinite loop (varnishadm.c:279) due to probably readline problem.

I made some mod resuming code pushed out from GH commit a5d5ecdea86ba6d9dcb036a78f7606c693f42190.

Don't know if it is the proper way.
Thanks for attention