Proper return value from 'swrite()' when connection has been closed

Proper return value from 'swrite()' when connection has been closed

According to POSIX, errno is set only if 'recv()' returns -1.
When connection has been closed, 'recv()' returns 0 and errno left untouched.
For functions which check errno value after 'swrite()', errno now is set to ECONNRESET,
so they produce correct message 'Connection reset by peer'.