Move signal into namespace util

signal will clash with the POSIX signal function. This tends to be too
annoying to work around with careful inclusion orders or other
namespacing.

signal.cpp

@@ -21,4 +21,4 @@
 #include "signal.hpp"
 
 // Instance something probably useful here so that we generate early compile/link errors.
-template class signal <void>;
+template class util::signal <void>;

signal.hpp

@@ -24,9 +24,9 @@
 #include <vector>
 #include <functional>
 
-
-template <typename Ret, typename ...Args>
-class signal {
+namespace util {
+    template <typename Ret, typename ...Args>
+    class signal {
         public:
             typedef Ret (*callback_function)(Args...);
             typedef std::function<Ret(Args...)> callback_object;
@@ -71,6 +71,7 @@ class signal {
                 for (auto i = m_children.begin (), end = m_children.end (); i != end; ++i)
                     (*i)(tail...);
             }
-};
+    };
+}
 
 #endif // __SIGNAL_HPP