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.

unittests/type_info_test.cpp

@@ -1,6 +1,7 @@
 // Tests to make sure that the order in which function dispatches occur is correct
 
 #include <chaiscript/dispatchkit/type_info.hpp>
+#include <cstdlib>
 
 void test_type(const chaiscript::Type_Info &ti, bool t_is_const, bool t_is_pointer, bool t_is_reference, bool t_is_void,
     bool t_is_undef)