Redirect some headers noticed by the compiler #64

/usr/include/sys/poll.h:1:2: warning: #warning redirecting incorrect #include <sys/poll.h> to <poll.h> [-Wcpp]
    1 | #warning redirecting incorrect #include <sys/poll.h> to <poll.h>
/usr/include/sys/signal.h:1:2: warning: #warning redirecting incorrect #include <sys/signal.h> to <signal.h> [-Wcpp]
    1 | #warning redirecting incorrect #include <sys/signal.h> to <signal.h>

Note: <sys/signal.h> has been removed from the tdeio/tdeio/connection.cpp source - it was already declared.

Here's an interesting situation with sys/poll.h × poll.h:

On Linux (glibc) poll.h contains #include <sys/poll.h>, so the real file is really in `sys/poll.h
On FreeBSD poll.h is symlink to sys/poll.h, so the real file is really in sys/poll.h.

The mentioned incorrect seems to be on many systems as a real true file location. That's why I'm a little hesitant about what's right.

In any case, the test on Debian and FreeBSD is without problems.

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/poll.h.html#tag_13_34

Please can you rebase to the current HEAD so that your GPG signature can be preserved when merged?

Done. 👍