Fixed bug #65184 strftime() returns insufficient-length

string under multibyte locales

The msdn doc states 'strftime returns the number of characters', but prior
to VS2012 it seems to have returned the number of bytes. Locale independent.
The return is however \0-terminated, so strlen is just fine. The behaivor
seems to be persisting in the later VC++ versions as the corresponding
MSDN ticket is closed 'by design'.

See http://connect.microsoft.com/VisualStudio/feedback/details/766205/vs2012-strftime-has-incorrect-return-value-in-vc-11-with-multibyte-codepages#details