fixed exports for vs 2013 express

As discussed in the thread on the mailing list with Karl and Nick here is a version that has all the missing exports fixed. Compiles cleanly for me (x64, debug/release) using vs 2013 express. I can not really check if any of my fixes break other Visual Studio versions.
Also added a "#define NOMINMAX" to ImfDwaCompressor to force std:: to work.