Issue 5249: Fix strftime on windows.

On windows, format string should be encoded as mbcs. Otherwise, result
of strftime would be broken. Here is the patch.

I think we should use wcsftime on Windows, even though it works very
similar to your patch (with the primary difference being that it uses
alloca instead of Py_Malloc).

I experimentally implemented with wcsftime, but I couldn't get same
result as strftime + mbcs conversion. Probably because wcsftime depends
on locale.

Sorry, if we use wcsftime, I cannot create the patch. On VC6, wcsftime
returns not unicode but mbcs string which copied to wchar array.

Maybe on snakebite.org, I can access VC9 and confirm its behavior on it? ;-)

> On VC6, wcsftime simply converts *format* to mbcs string, calls
> strftime, and converts result to unicode, so there is no difference
> between my patch and wcsftime.

Right.

> (Newer VC's wcsftime might have different
> implementation though) Maybe you are concerning about the cost of extra
> unicode object creation on non-windows platform? 

No. I'm concerned primarily about code cleanliness, by relying on
library code rather than implementing stuff ourselves.

OTOH, the conversion to narrow strings still needs to happen on Unix
(and probably needs to use the locale's encoding, not UTF-8), so
a uniform treatment also has a value.

Locale is my weak point. :-(
If there is locale encoding function like PyUnicode_DecodeFSDefault for
file system encoding, I think I can use it.

Using TZNAME_ENCODING is fine; I just think it has an incorrect value on
Unix.

All in all, I think the (original) patch is fine, please apply.

Thanks, fixed in r69664(py3k) and r69665(release30-maint).