Manual execution of linkchecker fails on URLs where curl faces timeout

[suankan]

Problem:
$ php admin/tool/task/cli/schedule_task.php --execute='\local_linkchecker_robot\task\crawl_task'
fails on this URL on which curl_exec() faces timeout 60 sec.

Attempted:
Added http://validator.w3.org/ and http://www.contentquality.com/ to local/linkchecker_robot/settings.php. See commit.
But the above CLI execution still stumbles on the same URL

This needs further looking into it.

[suankan]

For some reason I cannot reproduce this issue anymore.