Save options delay

Set how often IniFiles are saved (in seconds).

Those files are also saved on \"normal\" exit, so this setting only matters if MLdonkey may be interrupted abruptly (kill -9, system crash, power loss,...). In that case, lowering this setting should decrease the amount of \"recent events\" (setting changes, download bytes received, hashed chunks,...) that are forgotten, at the expense of some CPU and disk activity.