Made thread_pool's destructor call abort() rather than rethrow any exception to

avoid compiler warnings.

dlib/threads/thread_pool_extension.h

@@ -513,12 +513,16 @@ namespace dlib
             {
                 std::cerr << "An unhandled exception was inside a dlib::thread_pool when it was destructed." << std::endl;
                 std::cerr << "It's what string is: \n" << e.what() << std::endl;
-                throw;
+                using namespace std;
+                assert(false);
+                abort();
             }
             catch (...)
             {
                 std::cerr << "An unhandled exception was inside a dlib::thread_pool when it was destructed." << std::endl;
-                throw;
+                using namespace std;
+                assert(false);
+                abort();
             }
         }
 

dlib/threads/thread_pool_extension_abstract.h

@@ -251,6 +251,10 @@ namespace dlib
         /*!
             ensures
                 - blocks until all tasks in the pool have finished.
+                - If one of the threads has generated an exception but it hasn't yet been
+                  rethrown to the caller (e.g. by calling wait_for_all_tasks()) then the
+                  program will be terminated.  So make sure you handle all the possible
+                  exceptions from your tasks.
         !*/
 
         bool is_task_thread (