CSHARP-980:fixed issue with Kerberos corrupting managed memory.

Author: craiggwilson

MongoDB.Driver/Communication/Security/Mechanisms/Sspi/SecurityContext.cs

@@ -421,7 +421,7 @@ private static int GetMaxTokenSize()
             {
                 try
                 {
-                    Win32.FreeContextBuffer(ref array);
+                    Win32.FreeContextBuffer(array);
                 }
                 catch
                 { }

MongoDB.Driver/Communication/Security/Mechanisms/Sspi/Win32.cs

@@ -247,7 +247,7 @@ public static extern uint EncryptMessage(ref SspiHandle context,
         /// </remarks>
         [DllImport("security.dll", CharSet = CharSet.None)]
         [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
-        public static extern uint FreeContextBuffer(ref IntPtr contextBuffer);
+        public static extern uint FreeContextBuffer(IntPtr contextBuffer);
 
         /// <summary>
         /// Frees the credentials handle.