Suppress warning CS0420

Its ok to ignore CS0420 "a reference to a volatile field will not be treated as volatile" for interlocked calls, see http://msdn.microsoft.com/en-us/library/4bw5ewxy(VS.80).aspx
Merge pull request #176 from HCanber/supress-cs0420-warnings

Suppress warning CS0420 for Interlocked calls.

Its ok to ignore CS0420 "a reference to a volatile field will not be treated as volatile" for interlocked calls, see http://msdn.microsoft.com/en-us/library/4bw5ewxy(VS.80).aspx