Notification of string changes

Author: Eloy Lafuente (stronk7)
MDL-50182 core: add 3.0 environmental requirements
Only change from 2.9 is the modification of the slasharguments
admin setting string to recommend always to keep the setting enabled
and fix the problem in the server, warning about the drawbacks
of disabling it.

Also, there is a little phpdoc note added to one custom check
to have clearly specified when we can get rid of it.


http://git.moodle.org/gw?p=moodle.git;a=commit;h=ca09f076f8475b166e21c779f624b742292c7b06
http://github.com/moodle/moodle/commit/ca09f076f8475b166e21c779f624b742292c7b06

+ 3.0 en [configslasharguments,core_admin]