Notification of string changes

Author: David Mudrák
MDL-35238 Fetch available updates using the 1.1 version of the API
If the stored response has still 1.0 version (which is expected during
the upgrade to 2.4), a debugging message is displayed. Added a string to
explain what's going on and how to recover from the state.


http://git.moodle.org/gw?p=moodle.git;a=commit;h=85d751631328277b40ce88f4ed9cc67bb4494e96
http://github.com/moodle/moodle/commit/85d751631328277b40ce88f4ed9cc67bb4494e96

+ 2.4 en [err_response_format_version,core_plugin]