_readdir_pyx extension cannot be compiled with MSVC

[Alexander Belchenko]

building 'bzrlib._readdir_pyx' extension
c:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\bin\cl.exe /c /nologo /Ox /MD /W3 /GX /DNDEBUG 
-IC:\Python\2.5.1\include -IC:\Python\2.5.1\PC /Tcbzrlib/_readdir_pyx.c 
/Fobuild\temp.win32-2.5\Release\bzrlib/_readdir_pyx.obj
_readdir_pyx.c
bzrlib\_readdir_pyx.c(32) : fatal error C1083: Cannot open include file: 'dirent.h': No such file or directory
Building of "bzrlib._readdir_pyx" extension failed, will use the Python version instead