config, terminal, command: Add substitute-path parameter to configuration file. (#640)

Allows to rewrite a source path stored in program's debug information,
if the sources were moved to a different place between compilation and
debugging.

terminal/command.go

@@ -1252,7 +1252,7 @@ func printcontextThread(t *Term, th *api.Thread) {
 }
 
 func printfile(t *Term, filename string, line int, showArrow bool) error {
-	file, err := os.Open(filename)
+	file, err := os.Open(t.substitutePath(filename))
 	if err != nil {
 		return err
 	}