Fixes #88: Linking error on MacOS Mavericks

The c++ library implementation on MacOS is broken, it does not allow you to
correctly use points to members of std::string. We work around this by not
directly using member pointers and instead wrapping the method calls
with our own functions.

include/chaiscript/chaiscript_threading.hpp

@@ -84,6 +84,8 @@ namespace chaiscript
       {
         public:
           unique_lock(T &) {}
+          void lock() {}
+          void unlock() {}
       };
 
       template<typename T>
@@ -91,6 +93,7 @@ namespace chaiscript
       {
         public:
           shared_lock(T &) {}
+          void lock() {}
           void unlock() {}
       };