title: PHP module is already loaded warning
body: <p>Just noticed, that PHP throws warnings, when executed on the CLI:</p>
  
  <p>php module is already loaded</p>
  
  <pre><code>$ php -v
  PHP Warning:  Module 'PDO' already loaded in Unknown on line 0
  PHP Warning:  Module 'calendar' already loaded in Unknown on line 0
  PHP Warning:  Module 'ctype' already loaded in Unknown on line 0
  PHP Warning:  Module 'exif' already loaded in Unknown on line 0
  PHP Warning:  Module 'fileinfo' already loaded in Unknown on line 0
  PHP Warning:  Module 'ftp' already loaded in Unknown on line 0
  PHP Warning:  Module 'gettext' already loaded in Unknown on line 0
  PHP Warning:  Module 'iconv' already loaded in Unknown on line 0
  PHP Warning:  Module 'Phar' already loaded in Unknown on line 0
  PHP Warning:  Module 'posix' already loaded in Unknown on line 0
  PHP Warning:  Module 'shmop' already loaded in Unknown on line 0
  PHP Warning:  PHP Startup: Unable to load dynamic library '/usr/lib/php/20151012/sockets.so' - /usr/lib/php/20151012/sockets.so: undefined symbol: php_network_gethostbyname in Unknown on line 0
  PHP Warning:  Module 'sysvmsg' already loaded in Unknown on line 0
  PHP Warning:  Module 'sysvsem' already loaded in Unknown on line 0
  PHP Warning:  Module 'sysvshm' already loaded in Unknown on line 0
  PHP Warning:  Module 'tokenizer' already loaded in Unknown on line 0
  PHP 7.0.3-5+deb.sury.org~trusty+1 (cli) ( NTS )
  Copyright (c) 1997-2016 The PHP Group
  Zend Engine v3.0.0, Copyright (c) 1998-2016 Zend Technologies
      with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies
      with Xdebug v2.4.0RC4, Copyright (c) 2002-2016, by Derick Rethans
  </code></pre>
  
  <p>I know, how to prevent them -- simply remove <code>extension={extname}.so</code> from the <code>/etc/php/7.0/cli/conf.d/{extname}.ini</code> files. But:</p>
  
  <p><strong>Is removing of this line in the INI files a solution or just a workaround to avoid the warning messages? Can any side effects occur due to this? Why does it happen / What is the issue actually caused by?</strong></p>