Author: Stefan Hanauska
MDL-84611 blocks: Respect instance_allow_multiple()
http://git.moodle.org/gw?p=moodle.git;a=commit;h=172277eae4e7d67e0a840516f81049c0f1ddfc60
http://github.com/moodle/moodle/commit/172277eae4e7d67e0a840516f81049c0f1ddfc60
+ 4.5 en [blockcannotadd,core_error]