tools/ccanlint: add global .valgrind_suppressions file.

Seems like my local Ubuntu install is giving bogus warnings.  Allow
local valgrind overrides.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
ccan/io: fix io_connect.

getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &len) gives err == ECONNREFUSED
when connection is refused.  Handle this (and other error cases).

And we need F_SETFL not F_SETFD to restore blocking on the socket!

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>