To prevent warnings such as "ini_set() has been disabled for security reasons", we should set memory_limit by "@" call to prevent error displaying.

We can either put @ in the function itself to call @ini_set() - (my -1 against as it is one way ticket)
or to call @raise_memory_limit() - this is usually true except two calls from backup: see #2 and #3 in the following list:

Cscope tag: raise_memory_limit

1. line file
   1 73 admin/uploadpicture.php <<get_data>>
   @raise_memory_limit("192M");
   2 689 backup/lib.php <<array>>
   raise_memory_limit("192M");
   3 143 backup/restore.php <<basename>>
   raise_memory_limit("192M");
   4 98 grade/import/csv/index.php <<get_data>>
   @raise_memory_limit("192M");
   5 207 grade/import/csv/index.php <<get_data>>
   @raise_memory_limit("192M");
   6 57 grade/import/xml/index.php <<get_data>>
   @raise_memory_limit("256M");
   7 90 mod/data/import.php <<confirm_sesskey>>
   @raise_memory_limit("96M");