Added a .revert() to the locally_change_current_dir object.

dlib/misc_api/misc_api_kernel_abstract.h

@@ -90,6 +90,15 @@ namespace dlib
         );
         /*!
             ensures
+                - if (revert() hasn't already been called) then
+                    - calls set_current_dir(old_dir())
+        !*/
+
+        void revert (
+        );
+        /*!
+            ensures
+                - if (revert() hasn't already been called) then
                     - calls set_current_dir(old_dir())
         !*/
     };

dlib/misc_api/misc_api_shared.h

@@ -18,13 +18,14 @@ namespace dlib
             const std::string& new_dir
         )
         {
+            reverted = false;
             _old_dir = get_current_dir();
             set_current_dir(new_dir);
         }
 
         ~locally_change_current_dir()
         {
-            set_current_dir(_old_dir);
+            revert();
         }
 
         const std::string& old_dir (
@@ -33,7 +34,18 @@ namespace dlib
             return _old_dir;
         }
 
+        void revert (
+        )
+        {
+            if (!reverted)
+            {
+                set_current_dir(_old_dir);
+                reverted = true;
+            }
+        }
+
     private:
+        bool reverted;
         std::string _old_dir;
     };