Add description for new param

htdocs/core/lib/functions.lib.php

@@ -172,6 +172,8 @@ function dol_shutdown()
  *  @param	string	$paramname   Name of parameter to found
  *  @param	string	$check	     Type of check (''=no check,  'int'=check it's numeric, 'alpha'=check it's text and sign, 'aZ'=check it's a-z only, 'array'=check it's array, 'san_alpha'= Use filter_var with FILTER_SANITIZE_STRING, 'custom'= custom filter specify $filter and $options)
  *  @param	int		$method	     Type of method (0 = get then post, 1 = only get, 2 = only post, 3 = post then get, 4 = post then get then cookie)
+ *  @param  int     $filter      Filter to apply when $check is set to custom. (See http://php.net/manual/en/filter.filters.php for détails)
+ *  @param  mixed   $options     Options to pass to filter_var when $check is set to custom     
  *  @return string||string[]      		 Value found, or '' if check fails
  */
 function GETPOST($paramname,$check='',$method=0,$filter=NULL,$options=NULL)