osutil.c: include Python.h before the other headers

This is recommended by the Python documentation, since Python.h defines
some constants.

mercurial/osutil.c

@@ -9,6 +9,7 b''
 
 #define _ATFILE_SOURCE
 #define _LARGEFILE64_SOURCE
+#include <Python.h>
 #include <alloca.h>
 #include <dirent.h>
 #include <fcntl.h>
@@ -17,8 +18,6 b''
 #include <sys/types.h>
 #include <unistd.h>
 
-#include "Python.h"
-
 struct listdir_stat {
     PyObject_HEAD
     struct stat st;