* changes.txt: misc
Merge branch 'master' of github.com:facebook/pfff
* main_stags.ml: comment
* lang_php/analyze/foundation/graph_code_php.ml: memoize class_exists
* lang_php/analyze/foundation/builtins_php.ml: better
* lang_php/analyze/foundation/database_prolog_php.ml: capture TodoNamespace too