Renamed config.h -> jansson_private_config.h

This is because it's really easy to get a name collission if compiling
Jansson as a subproject in a larger CMake project. If one project includes
several subprojects each having their own config.h, this will cause the
wrong file to be loaded.

test/bin/json_process.c

@@ -6,7 +6,7 @@
  */
 
 #ifdef HAVE_CONFIG_H
-#include <config.h>
+#include <jansson_private_config.h>
 #endif
 
 #include <stdio.h>