> Also note that on platforms with 16-bit wchar_t, the comparison
> (0xffff < *w) will always be false, so an additional check for
> (Py_UNICODE_SIZE > 2) is needed.

Yes, but the right test is (SIZEOF_WCHAR_T > 2). I wrote a new test:

#if (Py_UNICODE_SIZE == 2) && (SIZEOF_WCHAR_T > 2)
#define USE_WCHAR_SURROGATE
    const wchar_t *orig_w;
#endif

> BTW: Please always use upper-case hex literals, or at leat don't
> mix the case within the same function.

I try, but it would be easier if the rule was already respected: they 
are many tabs and many lower-case hex literals. I used copy/paste from 
existing code of unicodeobject.c...

Patch version 3:
 - disable the UTF-16 surrogate for 16 bits wchar_t: so my patch is 
only used for 16 bits Py_UNICODE and 32 bits wchar_t... which is the 
default case for python 2.6 and 3.0 on Linux
 - replace tabulation by spaces (in existing code)
 - use upper case literals