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=503581b5d07a799185f19d633428eb2778cfa9ba
http://github.com/moodle/moodle/commit/503581b5d07a799185f19d633428eb2778cfa9ba
+ 2.0 en [invalidurl,mod_url]