More AdaSockets

Hi everyone

I don't know if Samuel Tardieu got my email, but I'll post that here
in case someone find it useful :)
I needed a poll function, so I made one which could be useful at some
point. I also made a Send_Some (same as receive_some), of which I'm
still wondering if it is truely useful or it's just a stupid idea of
mine (and in anycase, I need it, so I'll keep it). And finally, I also
adapted 2 functions from GNAT.Sockets : Get_Service_By_Name and
Port_Number.

I'd think a Poll function would be fine in AdaSockets :)

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--- specs :

with Ada.Streams;                use Ada.Streams;
with Sockets;                    use Sockets;

package More_AdaSockets is

   type Poll_Option is (POLLNULL,   -- nothing...
                        POLLIN,     -- There is data to read
                        POLLPRI,    -- There is urgent data to read
                        POLLOUT,    -- Writing now will not block
                        POLLERR,    -- Error condition
                        POLLHUP,    -- Hung up
                        POLLNVAL,   -- Invalid request: fd not open
                        -- When compiling XPG4.2 source also has
                        POLLRDNORM, -- Normal data may be read