use errno.h not sys/errno.h in utils.c as in other files (#207)

use errno.h not sys/errno.h in utils.c as in other files (#207)

Use errno.h rather than sysno/errno.h in utils.c, unbreaking build on OpenBSD (the "errno" symbol is only defined in errno.h not in sys/errno.h).

protocol.c and server.c already include errno.h rather than sys/errno.h so this should be safe on other OS here also.