Author: Ankit Kumar Agarwal
MDL-28483 URL adding validation checks and changing field externalurl to not-null
http://git.moodle.org/gw?p=moodle.git;a=commit;h=4373200f88cf235d08e9f5c81f252886036a822e
http://github.com/moodle/moodle/commit/4373200f88cf235d08e9f5c81f252886036a822e
+ 2.2 en [invalidurl,mod_url]