Author: Shamim Rezaie
MDL-43189 core: Validate db prefix during installation
http://git.moodle.org/gw?p=moodle.git;a=commit;h=7a902dea3a7c2ec4578c174e2ce9a54abe9e415f
http://github.com/moodle/moodle/commit/7a902dea3a7c2ec4578c174e2ce9a54abe9e415f
+ 3.6 en [invaliddbprefix,core_install]