Add includes and split off json_types.h to help ensure that headers can be included in any order.

vasprintf_compat.h

@@ -8,6 +8,8 @@
 
 #include "snprintf_compat.h"
 
+#include <malloc.h>
+
 #if !defined(HAVE_VASPRINTF)
 /* CAW: compliant version of vasprintf */
 static int vasprintf(char **buf, const char *fmt, va_list ap)