Updated as auto close timeout final
Using lexical_cast_default and with good indentation.

(file #15596)

Can you summarize which modifications left ?
Maybe the underscores ?

Updated with MaxDuration1.patch

(file #15487)

Some notes on coding conventions:
We like to have code written in a more-or-less same style.

non-public class member variables (and only them) should end in underscore (like 'max_duration_' when it is a class variables, and just 'max_duration' when it is a local variable or a method parameter)

So, use max_duration_ only when it is a class variable, and never use _max_duration

Also, watch the spacing - use only tabs, not spaces, to indent C++ code in wesnoth.

An implementation of duration, in frames. When a duration=X is specified in [message], the message will automatically dissapear after X frames. If the player click or press spacebar, the message can be skipped earlier.

Was requested here : https://gna.org/bugs/?func=detailitem&item_id=18483