chatter: use static function to control timestamping behavior

Use a static function instead of embedding side-effects in the constructor
of an unrelated class.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
(cherry picked from commit 85106bd9a9fb3be2c574df1a3aed6674e3951465)

include/crucible/chatter.h

@@ -45,6 +45,8 @@ namespace crucible {
 		template <class T> Chatter &operator<<(const T& arg);
 
 		~Chatter();
+
+		static void enable_timestamp(bool prefix_timestamp);
 	};
 
 	template <class Argument>
@@ -86,11 +88,6 @@ namespace crucible {
 		}
 	};
 
-	class ChatterTimestamp {
-	public:
-		ChatterTimestamp(int);
-	};
-
 	class ChatterBox {
 		string m_file;
 		int m_line;