Added HP-UX Serial port detection (for SHOW SERIAL) from  Mikulas Patocka
HP-UX socket fixes from Mikulas Patocka.

1. getaddrinfo returns IPv6 address even if IPv6 is not configured.
The socket syscalls fails to create IPv6 socket. This is fixed by retrying for all possible addresses returned by getaddrinfo.

2. On HP-UX EAGAIN is used, not EWOULDBLOCK.