Run check-includes.py script with detected python path.

Makefile.am

@@ -314,7 +314,7 @@ endif
 
 check-includes:
 if USEPYTHON
-	$(top_srcdir)/scripts/maint/checkIncludes.py
+	$(PYTHON) $(top_srcdir)/scripts/maint/checkIncludes.py
 endif
 
 check-docs: all