mod_ssl: follow up to r1705823.

Flush SSL/TLS handshake data when writing (instead of before reading),
and only when necessary (openssl < 0.9.8m or proxy/client side).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1707230 13f79535-47bb-0310-9956-ffa450edef68