Update to support building with MinGW #78

We cannot call MinGW a fully supported platform for C++11 yet:

 - Concurrency is not yet supported by MinGW, so it is disabled by default
 - A problem in the memory model / library loader is preventing derived type
   casts from working. This may be able to be worked around, but has not been
   yet.

samples/example.cpp

@@ -5,6 +5,7 @@
 // http://www.chaiscript.com
 
 #include <iostream>
+#include <ctime>
 
 #include <chaiscript/chaiscript.hpp>
 #include <chaiscript/dispatchkit/bootstrap_stl.hpp>