partial sync of regress/netcat.c with upstream

partial sync of regress/netcat.c with upstream

The code in socks.c writes multiple times in a row to a socket. If the socket becomes invalid between these calls (e.g. connection closed), write will throw SIGPIPE. With this patch, SIGPIPE is ignored so we can handle write's -1 return value (errno will be EPIPE). Ultimately, it leads to program exit, too -- but with nicer error message. :)

with input by and ok djm