Author: Ryan Wyllie
MDL-65394 portfolio: add cache for portfolio_add_button
http://git.moodle.org/gw?p=moodle.git;a=commit;h=76fbbf7e7e1b33e1606d2ec5722be68ac950dcc7
http://github.com/moodle/moodle/commit/76fbbf7e7e1b33e1606d2ec5722be68ac950dcc7
+ 3.7 en [cachedef_portfolio_add_button_portfolio_instances,core_cache]