python: Include <Python.h> first

Python is broken and requires that we include <Python.h> before all
other headers so it can make inadvisable definitions of
_POSIX_C_SOURCE and other things.  This wasn't a problem before, but a
recent change to glibc makes this necessary now.

See also a similar commit in nbdkit:
f924c3c34b

I also removed the -Wcast-align suppression as that is no longer
needed.

python/handle.c

@@ -22,6 +22,10 @@
  * F<python/actions-*.c>).
  */
 
+/* This must be included first. */
+#define PY_SSIZE_T_CLEAN 1
+#include <Python.h>
+
 #include <config.h>
 
 #include <stdio.h>