SSL: fixed shutdown handling. Previously, bidirectional shutdown never worked, due to two issues in the code: 1. The code only tested SSL_ERROR_WANT_READ and SSL_ERROR_WANT_WRITE when there was an error in the error queue, which cannot happen. The bug was introduced in an attempt to fix unexpected error logging as reported with OpenSSL 0.9.8g (http://mailman.nginx.org/pipermail/nginx/2008-January/003084.html). 2. The code never called SSL_shutdown() for the second time to wait for the peer's close_notify alert. This change fixes both issues. Note that after this change bidirectional shutdown is expected to work for the first time, so c->ssl->no_wait_shutdown now makes a difference. This is not a problem for HTTP code which always uses c->ssl->no_wait_shutdown, but might be a problem for stream and mail code, as well as 3rd party modules. To minimize the effect of the change, the timeout, which was used to be 30 seconds and not configurable, though never actually used, is now set to 3 seconds. It is also expanded to apply to both SSL_ERROR_WANT_READ and SSL_ERROR_WANT_WRITE, so timeout is properly set if writing to the socket buffer is not possible.