Merge branch 'jk/path-name-safety-2.4' into maint-2.4

Bugfix patches were backported from the 'master' front to plug heap corruption holes, to catch integer overflow in the computation of pathname lengths, and to get rid of the name_path API. Both of these would have resulted in writing over an under-allocated buffer when formulating pathnames while tree traversal. * jk/path-name-safety-2.4: list-objects: pass full pathname to callbacks list-objects: drop name_path entirely list-objects: convert name_path to a strbuf show_object_with_name: simplify by using path_name() http-push: stop using name_path tree-diff: catch integer overflow in combine_diff_path allocation add helpers for detecting size_t overflow