[boost] [signals2] Compile errors when using signals2

Hi, I had some compiling errors when I wanted to try out signals2. In predestructible.hpp line 33 there is an extra semicolon (the empty {} scope has a an extra ;). Also, in tracked_objects_visitor.hpp line 85, the "trackable" parameter is unused, which causes a warning. The warning is not critical, but the error is. It basically forces one to either manually fix the predestructible.hpp header, or to stop using the -pedantic flag. My flags: -Wextra -Wall -std=c++98 -pedantic