Add a way to enable renegotiation in QSSLSocket

OpenSSL >= 0.9.8l disable renegotiation by default: http://isc.sans.org/diary.html?storyid=7543
You can still enable it:

• OpenSSL = 0.9.8I SSL3_FLAGS_ALLOW_UNSAFE_LEGACY_RENEGOTIATION in s3->flags
• OpenSSL > 0.9.8l SSL_CTX_set_options(ssl_ctx, SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION)

There should be a way to do that in Qt.
Maybe a more flexible way would be add a method which return the SSL_CTX (like the QAbstractSocket::socketDescriptor() method which return the fd).