GetFullPathNameW may return the required buffer size (non-zero value) 
when buffer is too short. Before r67154, this case was treated as 
success, so there was possibility of access to uninitialized buffer 
woutbuf. Fortunately, GetFullPathNameW sets '\0' to woutbuf (this is 
undocumented behavior), so abspath() returned empty string instead of 
segmentation fault. But this is still potentially dangerous, so I fixed 
this by allocating required size buffer and calling GetFullPathNameW 
again. abspath() returns correct result for any long unicode path now.

But original poster hopes abspath() should return correct result for 
any long both *str* and unicode path. For str, this issue is not solved 
yet.

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I'm skeptical abspath() should support longer path than MAX_PATH if 
ANSI version of Windows API cannot handle such path. Anyway, I won't 
use such long path. ;-)