Add function to send signals to threads

include/fc/thread/thread.hpp

@@ -131,6 +131,11 @@ namespace fc {
        *  @todo make quit non-blocking of the calling thread by eliminating the call to <code>boost::thread::join</code>
        */
       void quit();
+
+      /**
+       * Send signal to underlying native thread. Only for Linux and macOS
+       */
+      void signal(int);
      
       /**
        *  @return true unless quit() has been called.

src/thread/thread.cpp

@@ -156,6 +156,17 @@ namespace fc {
 
    void          thread::debug( const fc::string& d ) { /*my->debug(d);*/ }
 
+#if defined(__linux__) || defined(__APPLE__)
+#include <signal.h>
+#endif
+
+   void thread::signal(int sig)
+   {
+#if defined(__linux__) || defined(__APPLE__)
+      pthread_kill( my->boost_thread->native_handle(), sig );
+#endif
+   }
+
   void thread::quit()
   {
     //if quitting from a different thread, start quit task on thread.