There is not only chown! There are also lchown(), fchown(), stat() and 
lstat().

Attached patch:
 - use "unsigned int" to store Windows st_uid/st_gid in the win32_stat 
structure
 - use PyLong to store an unsigned group in the stat result (because 
2^32-2 doesn't fit in a PyInt)
 - use "unsigned int" (instead of long) for uid/gid in chown, lchown 
and fchown

Note: *chown() accepts -1 for an argument, eg. chown("file", 10, -1) 
only changes the user group.