Avoid a warning
common: initialize std output as early as possible

Even do it twice so that debugging messages can be output during early
initialization.
common: define WINVER to enable functions available only with Windows 2000 and later
Windows: use GetUserDefaultUILanguage() in order to determine default interface language

Implements #852.
Avoid a warning about uninitialized vars in recursive lambda
ChangeLog update
mmg: fix split by chapter arg validation for multiple-digit chapter numbers
mmg: signal D&D completion before processing the dropped files