poll: shouldn't it be sys/poll.h?

[Simon Josefsson]

I noticed in Shishi that I conditionally check for sys/poll.h, which
wouldn't be needed if I used the poll module.  However, it creates a
header file poll.h instead of sys/poll.h.  Is this intentional?  I can
provide a patch to move it if you want.

Btw, Shishi doesn't ever call the poll function, so maybe I don't need
to include that header file, or the gnulib poll module should be
separate from a new sys_poll module that only provides the header file.
I think I'll try to remove the include test in Shishi and see if it
breaks on some platform.

/Simon