Description:
------------
If a plugin alters the connection methods table, then the original connection 
table is not restored if there is a php_module_shutdown()/php_module_init() cycle 
in the same process.

This is because mysqlnd_conn_methods is a pointer to 
MYSQLND_CLASS_METHOD_TABLE_NAME(mysqlnd_conn), sizeof(mysqlnd_conn_methods)) so 
changing the values in mysqlnd_conn_methods actually changes the values in the 
master table.

To fix, mysqlnd_conn_methods should take a copy of the table on init.

Test script:
---------------
Create a plugin that replaces the conenct function with a function that simply flows the call to the original callback.

static enum_func_status
MYSQLND_METHOD(my_test_plugin, query)(MYSQLND* conn,
    const char* query, unsigned int query_len TSRMLS_DC) {
  return original_conn_methods.query(conn, query, query_len);
}

Register this plugin during MINIT


  struct st_mysqlnd_conn_methods* current_conn_methods =
      mysqlnd_conn_get_methods();

  memcpy(&original_conn_methods,
         current_conn_methods,
         sizeof(st_mysqlnd_conn_methods));

  current_conn_methods->connect = MYSQLND_METHOD(speckle_mysqlnd_conn, connect);

Start/Stop/Start the php modules

php_module_startup(...)
php_module_shutdown(...)
php_module_startup(...)

Try and connect to the mysqldb - you'll get a stack overflow.