Mark the testSslOption method as introduced in Qt 4.8

Change-Id: Ibe7cb1ca9cdcedd3f09dd4f865907e3f0fa6aef3
Reviewed-by: Richard J. Moore <rich@kde.org>
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>

src/network/ssl/qsslconfiguration.cpp

@@ -525,6 +525,8 @@ void QSslConfiguration::setSslOption(QSsl::SslOption option, bool on)
 }
 
 /*!
+  \since 4.8
+
   Returns true if the specified SSL compatibility option is enabled.
 
   \sa testSSlOption()