This allows $cfg->maxusercsvlines to be specified in config.php to
stop admins and institutional admins from uploading large csv files.
This is potentially useful on large multi-user sites.

And until such time as we can reduce the amount of memory used by the
create_user function, setting this option will provide the user with
some feedback on csv upload failure (because we can't easily trap the
php out-of-memory error).

See also bug #548042.

This commit also adds a call to set_time_limit() after processing each
user, so that the script doesn't fail due to php's max. execution
time.

Change-Id: I662231288c7d0c6e70602c548123f12c63427a97
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>